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 <sys/mman.h>
  13 #include <fcntl.h>
  14 #include <stdio.h>
  15 #include <stdlib.h>
  16 #include <string.h>
  17 #include <unistd.h>
  18 #include <errno.h>
  19 #include <objtool/builtin.h>
  20
  21 #include <objtool/elf.h>
  22 #include <objtool/warn.h>
  23
  24 #define MAX_NAME_LEN 128
  25
  26 static inline u32 str_hash(const char *str)
  27 {
  28         return jhash(str, strlen(str), 0);
  29 }
  30
  31 #define __elf_table(name)       (elf->name##_hash)
  32 #define __elf_bits(name)        (elf->name##_bits)
  33
  34 #define elf_hash_add(name, node, key) \
  35         hlist_add_head(node, &__elf_table(name)[hash_min(key, __elf_bits(name))])
  36
  37 #define elf_hash_for_each_possible(name, obj, member, key) \
  38         hlist_for_each_entry(obj, &__elf_table(name)[hash_min(key, __elf_bits(name))], member)
  39
  40 #define elf_alloc_hash(name, size) \
  41 ({ \
  42         __elf_bits(name) = max(10, ilog2(size)); \
  43         __elf_table(name) = mmap(NULL, sizeof(struct hlist_head) << __elf_bits(name), \
  44                                  PROT_READ|PROT_WRITE, \
  45                                  MAP_PRIVATE|MAP_ANON, -1, 0); \
  46         if (__elf_table(name) == (void *)-1L) { \
  47                 WARN("mmap fail " #name); \
  48                 __elf_table(name) = NULL; \
  49         } \
  50         __elf_table(name); \
  51 })
  52
  53 static bool symbol_to_offset(struct rb_node *a, const struct rb_node *b)
  54 {
  55         struct symbol *sa = rb_entry(a, struct symbol, node);
  56         struct symbol *sb = rb_entry(b, struct symbol, node);
  57
  58         if (sa->offset < sb->offset)
  59                 return true;
  60         if (sa->offset > sb->offset)
  61                 return false;
  62
  63         if (sa->len < sb->len)
  64                 return true;
  65         if (sa->len > sb->len)
  66                 return false;
  67
  68         sa->alias = sb;
  69
  70         return false;
  71 }
  72
  73 static int symbol_by_offset(const void *key, const struct rb_node *node)
  74 {
  75         const struct symbol *s = rb_entry(node, struct symbol, node);
  76         const unsigned long *o = key;
  77
  78         if (*o < s->offset)
  79                 return -1;
  80         if (*o >= s->offset + s->len)
  81                 return 1;
  82
  83         return 0;
  84 }
  85
  86 struct section *find_section_by_name(const struct elf *elf, const char *name)
  87 {
  88         struct section *sec;
  89
  90         elf_hash_for_each_possible(section_name, sec, name_hash, str_hash(name)) {
  91                 if (!strcmp(sec->name, name))
  92                         return sec;
  93         }
  94
  95         return NULL;
  96 }
  97
  98 static struct section *find_section_by_index(struct elf *elf,
  99                                              unsigned int idx)
 100 {
 101         struct section *sec;
 102
 103         elf_hash_for_each_possible(section, sec, hash, idx) {
 104                 if (sec->idx == idx)
 105                         return sec;
 106         }
 107
 108         return NULL;
 109 }
 110
 111 static struct symbol *find_symbol_by_index(struct elf *elf, unsigned int idx)
 112 {
 113         struct symbol *sym;
 114
 115         elf_hash_for_each_possible(symbol, sym, hash, idx) {
 116                 if (sym->idx == idx)
 117                         return sym;
 118         }
 119
 120         return NULL;
 121 }
 122
 123 struct symbol *find_symbol_by_offset(struct section *sec, unsigned long offset)
 124 {
 125         struct rb_node *node;
 126
 127         rb_for_each(node, &offset, &sec->symbol_tree, symbol_by_offset) {
 128                 struct symbol *s = rb_entry(node, struct symbol, node);
 129
 130                 if (s->offset == offset && s->type != STT_SECTION)
 131                         return s;
 132         }
 133
 134         return NULL;
 135 }
 136
 137 struct symbol *find_func_by_offset(struct section *sec, unsigned long offset)
 138 {
 139         struct rb_node *node;
 140
 141         rb_for_each(node, &offset, &sec->symbol_tree, symbol_by_offset) {
 142                 struct symbol *s = rb_entry(node, struct symbol, node);
 143
 144                 if (s->offset == offset && s->type == STT_FUNC)
 145                         return s;
 146         }
 147
 148         return NULL;
 149 }
 150
 151 struct symbol *find_symbol_containing(const struct section *sec, unsigned long offset)
 152 {
 153         struct rb_node *node;
 154
 155         rb_for_each(node, &offset, &sec->symbol_tree, symbol_by_offset) {
 156                 struct symbol *s = rb_entry(node, struct symbol, node);
 157
 158                 if (s->type != STT_SECTION)
 159                         return s;
 160         }
 161
 162         return NULL;
 163 }
 164
 165 struct symbol *find_func_containing(struct section *sec, unsigned long offset)
 166 {
 167         struct rb_node *node;
 168
 169         rb_for_each(node, &offset, &sec->symbol_tree, symbol_by_offset) {
 170                 struct symbol *s = rb_entry(node, struct symbol, node);
 171
 172                 if (s->type == STT_FUNC)
 173                         return s;
 174         }
 175
 176         return NULL;
 177 }
 178
 179 struct symbol *find_symbol_by_name(const struct elf *elf, const char *name)
 180 {
 181         struct symbol *sym;
 182
 183         elf_hash_for_each_possible(symbol_name, sym, name_hash, str_hash(name)) {
 184                 if (!strcmp(sym->name, name))
 185                         return sym;
 186         }
 187
 188         return NULL;
 189 }
 190
 191 struct reloc *find_reloc_by_dest_range(const struct elf *elf, struct section *sec,
 192                                      unsigned long offset, unsigned int len)
 193 {
 194         struct reloc *reloc, *r = NULL;
 195         unsigned long o;
 196
 197         if (!sec->reloc)
 198                 return NULL;
 199
 200         sec = sec->reloc;
 201
 202         for_offset_range(o, offset, offset + len) {
 203                 elf_hash_for_each_possible(reloc, reloc, hash,
 204                                            sec_offset_hash(sec, o)) {
 205                         if (reloc->sec != sec)
 206                                 continue;
 207
 208                         if (reloc->offset >= offset && reloc->offset < offset + len) {
 209                                 if (!r || reloc->offset < r->offset)
 210                                         r = reloc;
 211                         }
 212                 }
 213                 if (r)
 214                         return r;
 215         }
 216
 217         return NULL;
 218 }
 219
 220 struct reloc *find_reloc_by_dest(const struct elf *elf, struct section *sec, unsigned long offset)
 221 {
 222         return find_reloc_by_dest_range(elf, sec, offset, 1);
 223 }
 224
 225 static int read_sections(struct elf *elf)
 226 {
 227         Elf_Scn *s = NULL;
 228         struct section *sec;
 229         size_t shstrndx, sections_nr;
 230         int i;
 231
 232         if (elf_getshdrnum(elf->elf, &sections_nr)) {
 233                 WARN_ELF("elf_getshdrnum");
 234                 return -1;
 235         }
 236
 237         if (elf_getshdrstrndx(elf->elf, &shstrndx)) {
 238                 WARN_ELF("elf_getshdrstrndx");
 239                 return -1;
 240         }
 241
 242         if (!elf_alloc_hash(section, sections_nr) ||
 243             !elf_alloc_hash(section_name, sections_nr))
 244                 return -1;
 245
 246         for (i = 0; i < sections_nr; i++) {
 247                 sec = malloc(sizeof(*sec));
 248                 if (!sec) {
 249                         perror("malloc");
 250                         return -1;
 251                 }
 252                 memset(sec, 0, sizeof(*sec));
 253
 254                 INIT_LIST_HEAD(&sec->symbol_list);
 255                 INIT_LIST_HEAD(&sec->reloc_list);
 256
 257                 s = elf_getscn(elf->elf, i);
 258                 if (!s) {
 259                         WARN_ELF("elf_getscn");
 260                         return -1;
 261                 }
 262
 263                 sec->idx = elf_ndxscn(s);
 264
 265                 if (!gelf_getshdr(s, &sec->sh)) {
 266                         WARN_ELF("gelf_getshdr");
 267                         return -1;
 268                 }
 269
 270                 sec->name = elf_strptr(elf->elf, shstrndx, sec->sh.sh_name);
 271                 if (!sec->name) {
 272                         WARN_ELF("elf_strptr");
 273                         return -1;
 274                 }
 275
 276                 if (sec->sh.sh_size != 0) {
 277                         sec->data = elf_getdata(s, NULL);
 278                         if (!sec->data) {
 279                                 WARN_ELF("elf_getdata");
 280                                 return -1;
 281                         }
 282                         if (sec->data->d_off != 0 ||
 283                             sec->data->d_size != sec->sh.sh_size) {
 284                                 WARN("unexpected data attributes for %s",
 285                                      sec->name);
 286                                 return -1;
 287                         }
 288                 }
 289
 290                 if (sec->sh.sh_flags & SHF_EXECINSTR)
 291                         elf->text_size += sec->sh.sh_size;
 292
 293                 list_add_tail(&sec->list, &elf->sections);
 294                 elf_hash_add(section, &sec->hash, sec->idx);
 295                 elf_hash_add(section_name, &sec->name_hash, str_hash(sec->name));
 296         }
 297
 298         if (stats) {
 299                 printf("nr_sections: %lu\n", (unsigned long)sections_nr);
 300                 printf("section_bits: %d\n", elf->section_bits);
 301         }
 302
 303         /* sanity check, one more call to elf_nextscn() should return NULL */
 304         if (elf_nextscn(elf->elf, s)) {
 305                 WARN("section entry mismatch");
 306                 return -1;
 307         }
 308
 309         return 0;
 310 }
 311
 312 static void elf_add_symbol(struct elf *elf, struct symbol *sym)
 313 {
 314         struct list_head *entry;
 315         struct rb_node *pnode;
 316
 317         sym->type = GELF_ST_TYPE(sym->sym.st_info);
 318         sym->bind = GELF_ST_BIND(sym->sym.st_info);
 319
 320         sym->offset = sym->sym.st_value;
 321         sym->len = sym->sym.st_size;
 322
 323         rb_add(&sym->node, &sym->sec->symbol_tree, symbol_to_offset);
 324         pnode = rb_prev(&sym->node);
 325         if (pnode)
 326                 entry = &rb_entry(pnode, struct symbol, node)->list;
 327         else
 328                 entry = &sym->sec->symbol_list;
 329         list_add(&sym->list, entry);
 330         elf_hash_add(symbol, &sym->hash, sym->idx);
 331         elf_hash_add(symbol_name, &sym->name_hash, str_hash(sym->name));
 332
 333         /*
 334          * Don't store empty STT_NOTYPE symbols in the rbtree.  They
 335          * can exist within a function, confusing the sorting.
 336          */
 337         if (!sym->len)
 338                 rb_erase(&sym->node, &sym->sec->symbol_tree);
 339 }
 340
 341 static int read_symbols(struct elf *elf)
 342 {
 343         struct section *symtab, *symtab_shndx, *sec;
 344         struct symbol *sym, *pfunc;
 345         int symbols_nr, i;
 346         char *coldstr;
 347         Elf_Data *shndx_data = NULL;
 348         Elf32_Word shndx;
 349
 350         symtab = find_section_by_name(elf, ".symtab");
 351         if (symtab) {
 352                 symtab_shndx = find_section_by_name(elf, ".symtab_shndx");
 353                 if (symtab_shndx)
 354                         shndx_data = symtab_shndx->data;
 355
 356                 symbols_nr = symtab->sh.sh_size / symtab->sh.sh_entsize;
 357         } else {
 358                 /*
 359                  * A missing symbol table is actually possible if it's an empty
 360                  * .o file. This can happen for thunk_64.o. Make sure to at
 361                  * least allocate the symbol hash tables so we can do symbol
 362                  * lookups without crashing.
 363                  */
 364                 symbols_nr = 0;
 365         }
 366
 367         if (!elf_alloc_hash(symbol, symbols_nr) ||
 368             !elf_alloc_hash(symbol_name, symbols_nr))
 369                 return -1;
 370
 371         for (i = 0; i < symbols_nr; i++) {
 372                 sym = malloc(sizeof(*sym));
 373                 if (!sym) {
 374                         perror("malloc");
 375                         return -1;
 376                 }
 377                 memset(sym, 0, sizeof(*sym));
 378                 sym->alias = sym;
 379
 380                 sym->idx = i;
 381
 382                 if (!gelf_getsymshndx(symtab->data, shndx_data, i, &sym->sym,
 383                                       &shndx)) {
 384                         WARN_ELF("gelf_getsymshndx");
 385                         goto err;
 386                 }
 387
 388                 sym->name = elf_strptr(elf->elf, symtab->sh.sh_link,
 389                                        sym->sym.st_name);
 390                 if (!sym->name) {
 391                         WARN_ELF("elf_strptr");
 392                         goto err;
 393                 }
 394
 395                 if ((sym->sym.st_shndx > SHN_UNDEF &&
 396                      sym->sym.st_shndx < SHN_LORESERVE) ||
 397                     (shndx_data && sym->sym.st_shndx == SHN_XINDEX)) {
 398                         if (sym->sym.st_shndx != SHN_XINDEX)
 399                                 shndx = sym->sym.st_shndx;
 400
 401                         sym->sec = find_section_by_index(elf, shndx);
 402                         if (!sym->sec) {
 403                                 WARN("couldn't find section for symbol %s",
 404                                      sym->name);
 405                                 goto err;
 406                         }
 407                         if (GELF_ST_TYPE(sym->sym.st_info) == STT_SECTION) {
 408                                 sym->name = sym->sec->name;
 409                                 sym->sec->sym = sym;
 410                         }
 411                 } else
 412                         sym->sec = find_section_by_index(elf, 0);
 413
 414                 elf_add_symbol(elf, sym);
 415         }
 416
 417         if (stats) {
 418                 printf("nr_symbols: %lu\n", (unsigned long)symbols_nr);
 419                 printf("symbol_bits: %d\n", elf->symbol_bits);
 420         }
 421
 422         /* Create parent/child links for any cold subfunctions */
 423         list_for_each_entry(sec, &elf->sections, list) {
 424                 list_for_each_entry(sym, &sec->symbol_list, list) {
 425                         char pname[MAX_NAME_LEN + 1];
 426                         size_t pnamelen;
 427                         if (sym->type != STT_FUNC)
 428                                 continue;
 429
 430                         if (sym->pfunc == NULL)
 431                                 sym->pfunc = sym;
 432
 433                         if (sym->cfunc == NULL)
 434                                 sym->cfunc = sym;
 435
 436                         coldstr = strstr(sym->name, ".cold");
 437                         if (!coldstr)
 438                                 continue;
 439
 440                         pnamelen = coldstr - sym->name;
 441                         if (pnamelen > MAX_NAME_LEN) {
 442                                 WARN("%s(): parent function name exceeds maximum length of %d characters",
 443                                      sym->name, MAX_NAME_LEN);
 444                                 return -1;
 445                         }
 446
 447                         strncpy(pname, sym->name, pnamelen);
 448                         pname[pnamelen] = '\0';
 449                         pfunc = find_symbol_by_name(elf, pname);
 450
 451                         if (!pfunc) {
 452                                 WARN("%s(): can't find parent function",
 453                                      sym->name);
 454                                 return -1;
 455                         }
 456
 457                         sym->pfunc = pfunc;
 458                         pfunc->cfunc = sym;
 459
 460                         /*
 461                          * Unfortunately, -fnoreorder-functions puts the child
 462                          * inside the parent.  Remove the overlap so we can
 463                          * have sane assumptions.
 464                          *
 465                          * Note that pfunc->len now no longer matches
 466                          * pfunc->sym.st_size.
 467                          */
 468                         if (sym->sec == pfunc->sec &&
 469                             sym->offset >= pfunc->offset &&
 470                             sym->offset + sym->len == pfunc->offset + pfunc->len) {
 471                                 pfunc->len -= sym->len;
 472                         }
 473                 }
 474         }
 475
 476         return 0;
 477
 478 err:
 479         free(sym);
 480         return -1;
 481 }
 482
 483 static struct section *elf_create_reloc_section(struct elf *elf,
 484                                                 struct section *base,
 485                                                 int reltype);
 486
 487 int elf_add_reloc(struct elf *elf, struct section *sec, unsigned long offset,
 488                   unsigned int type, struct symbol *sym, int addend)
 489 {
 490         struct reloc *reloc;
 491
 492         if (!sec->reloc && !elf_create_reloc_section(elf, sec, SHT_RELA))
 493                 return -1;
 494
 495         reloc = malloc(sizeof(*reloc));
 496         if (!reloc) {
 497                 perror("malloc");
 498                 return -1;
 499         }
 500         memset(reloc, 0, sizeof(*reloc));
 501
 502         reloc->sec = sec->reloc;
 503         reloc->offset = offset;
 504         reloc->type = type;
 505         reloc->sym = sym;
 506         reloc->addend = addend;
 507
 508         list_add_tail(&reloc->list, &sec->reloc->reloc_list);
 509         elf_hash_add(reloc, &reloc->hash, reloc_hash(reloc));
 510
 511         sec->reloc->sh.sh_size += sec->reloc->sh.sh_entsize;
 512         sec->reloc->changed = true;
 513
 514         return 0;
 515 }
 516
 517 int elf_add_reloc_to_insn(struct elf *elf, struct section *sec,
 518                           unsigned long offset, unsigned int type,
 519                           struct section *insn_sec, unsigned long insn_off)
 520 {
 521         struct symbol *sym;
 522         int addend;
 523
 524         if (insn_sec->sym) {
 525                 sym = insn_sec->sym;
 526                 addend = insn_off;
 527
 528         } else {
 529                 /*
 530                  * The Clang assembler strips section symbols, so we have to
 531                  * reference the function symbol instead:
 532                  */
 533                 sym = find_symbol_containing(insn_sec, insn_off);
 534                 if (!sym) {
 535                         /*
 536                          * Hack alert.  This happens when we need to reference
 537                          * the NOP pad insn immediately after the function.
 538                          */
 539                         sym = find_symbol_containing(insn_sec, insn_off - 1);
 540                 }
 541
 542                 if (!sym) {
 543                         WARN("can't find symbol containing %s+0x%lx", insn_sec->name, insn_off);
 544                         return -1;
 545                 }
 546
 547                 addend = insn_off - sym->offset;
 548         }
 549
 550         return elf_add_reloc(elf, sec, offset, type, sym, addend);
 551 }
 552
 553 static int read_rel_reloc(struct section *sec, int i, struct reloc *reloc, unsigned int *symndx)
 554 {
 555         if (!gelf_getrel(sec->data, i, &reloc->rel)) {
 556                 WARN_ELF("gelf_getrel");
 557                 return -1;
 558         }
 559         reloc->type = GELF_R_TYPE(reloc->rel.r_info);
 560         reloc->addend = 0;
 561         reloc->offset = reloc->rel.r_offset;
 562         *symndx = GELF_R_SYM(reloc->rel.r_info);
 563         return 0;
 564 }
 565
 566 static int read_rela_reloc(struct section *sec, int i, struct reloc *reloc, unsigned int *symndx)
 567 {
 568         if (!gelf_getrela(sec->data, i, &reloc->rela)) {
 569                 WARN_ELF("gelf_getrela");
 570                 return -1;
 571         }
 572         reloc->type = GELF_R_TYPE(reloc->rela.r_info);
 573         reloc->addend = reloc->rela.r_addend;
 574         reloc->offset = reloc->rela.r_offset;
 575         *symndx = GELF_R_SYM(reloc->rela.r_info);
 576         return 0;
 577 }
 578
 579 static int read_relocs(struct elf *elf)
 580 {
 581         struct section *sec;
 582         struct reloc *reloc;
 583         int i;
 584         unsigned int symndx;
 585         unsigned long nr_reloc, max_reloc = 0, tot_reloc = 0;
 586
 587         if (!elf_alloc_hash(reloc, elf->text_size / 16))
 588                 return -1;
 589
 590         list_for_each_entry(sec, &elf->sections, list) {
 591                 if ((sec->sh.sh_type != SHT_RELA) &&
 592                     (sec->sh.sh_type != SHT_REL))
 593                         continue;
 594
 595                 sec->base = find_section_by_index(elf, sec->sh.sh_info);
 596                 if (!sec->base) {
 597                         WARN("can't find base section for reloc section %s",
 598                              sec->name);
 599                         return -1;
 600                 }
 601
 602                 sec->base->reloc = sec;
 603
 604                 nr_reloc = 0;
 605                 for (i = 0; i < sec->sh.sh_size / sec->sh.sh_entsize; i++) {
 606                         reloc = malloc(sizeof(*reloc));
 607                         if (!reloc) {
 608                                 perror("malloc");
 609                                 return -1;
 610                         }
 611                         memset(reloc, 0, sizeof(*reloc));
 612                         switch (sec->sh.sh_type) {
 613                         case SHT_REL:
 614                                 if (read_rel_reloc(sec, i, reloc, &symndx))
 615                                         return -1;
 616                                 break;
 617                         case SHT_RELA:
 618                                 if (read_rela_reloc(sec, i, reloc, &symndx))
 619                                         return -1;
 620                                 break;
 621                         default: return -1;
 622                         }
 623
 624                         reloc->sec = sec;
 625                         reloc->idx = i;
 626                         reloc->sym = find_symbol_by_index(elf, symndx);
 627                         if (!reloc->sym) {
 628                                 WARN("can't find reloc entry symbol %d for %s",
 629                                      symndx, sec->name);
 630                                 return -1;
 631                         }
 632
 633                         list_add_tail(&reloc->list, &sec->reloc_list);
 634                         elf_hash_add(reloc, &reloc->hash, reloc_hash(reloc));
 635
 636                         nr_reloc++;
 637                 }
 638                 max_reloc = max(max_reloc, nr_reloc);
 639                 tot_reloc += nr_reloc;
 640         }
 641
 642         if (stats) {
 643                 printf("max_reloc: %lu\n", max_reloc);
 644                 printf("tot_reloc: %lu\n", tot_reloc);
 645                 printf("reloc_bits: %d\n", elf->reloc_bits);
 646         }
 647
 648         return 0;
 649 }
 650
 651 struct elf *elf_open_read(const char *name, int flags)
 652 {
 653         struct elf *elf;
 654         Elf_Cmd cmd;
 655
 656         elf_version(EV_CURRENT);
 657
 658         elf = malloc(sizeof(*elf));
 659         if (!elf) {
 660                 perror("malloc");
 661                 return NULL;
 662         }
 663         memset(elf, 0, offsetof(struct elf, sections));
 664
 665         INIT_LIST_HEAD(&elf->sections);
 666
 667         elf->fd = open(name, flags);
 668         if (elf->fd == -1) {
 669                 fprintf(stderr, "objtool: Can't open '%s': %s\n",
 670                         name, strerror(errno));
 671                 goto err;
 672         }
 673
 674         if ((flags & O_ACCMODE) == O_RDONLY)
 675                 cmd = ELF_C_READ_MMAP;
 676         else if ((flags & O_ACCMODE) == O_RDWR)
 677                 cmd = ELF_C_RDWR;
 678         else /* O_WRONLY */
 679                 cmd = ELF_C_WRITE;
 680
 681         elf->elf = elf_begin(elf->fd, cmd, NULL);
 682         if (!elf->elf) {
 683                 WARN_ELF("elf_begin");
 684                 goto err;
 685         }
 686
 687         if (!gelf_getehdr(elf->elf, &elf->ehdr)) {
 688                 WARN_ELF("gelf_getehdr");
 689                 goto err;
 690         }
 691
 692         if (read_sections(elf))
 693                 goto err;
 694
 695         if (read_symbols(elf))
 696                 goto err;
 697
 698         if (read_relocs(elf))
 699                 goto err;
 700
 701         return elf;
 702
 703 err:
 704         elf_close(elf);
 705         return NULL;
 706 }
 707
 708 static int elf_add_string(struct elf *elf, struct section *strtab, char *str)
 709 {
 710         Elf_Data *data;
 711         Elf_Scn *s;
 712         int len;
 713
 714         if (!strtab)
 715                 strtab = find_section_by_name(elf, ".strtab");
 716         if (!strtab) {
 717                 WARN("can't find .strtab section");
 718                 return -1;
 719         }
 720
 721         s = elf_getscn(elf->elf, strtab->idx);
 722         if (!s) {
 723                 WARN_ELF("elf_getscn");
 724                 return -1;
 725         }
 726
 727         data = elf_newdata(s);
 728         if (!data) {
 729                 WARN_ELF("elf_newdata");
 730                 return -1;
 731         }
 732
 733         data->d_buf = str;
 734         data->d_size = strlen(str) + 1;
 735         data->d_align = 1;
 736
 737         len = strtab->sh.sh_size;
 738         strtab->sh.sh_size += data->d_size;
 739         strtab->changed = true;
 740
 741         return len;
 742 }
 743
 744 struct symbol *elf_create_undef_symbol(struct elf *elf, const char *name)
 745 {
 746         struct section *symtab, *symtab_shndx;
 747         struct symbol *sym;
 748         Elf_Data *data;
 749         Elf_Scn *s;
 750
 751         sym = malloc(sizeof(*sym));
 752         if (!sym) {
 753                 perror("malloc");
 754                 return NULL;
 755         }
 756         memset(sym, 0, sizeof(*sym));
 757
 758         sym->name = strdup(name);
 759
 760         sym->sym.st_name = elf_add_string(elf, NULL, sym->name);
 761         if (sym->sym.st_name == -1)
 762                 return NULL;
 763
 764         sym->sym.st_info = GELF_ST_INFO(STB_GLOBAL, STT_NOTYPE);
 765         // st_other 0
 766         // st_shndx 0
 767         // st_value 0
 768         // st_size 0
 769
 770         symtab = find_section_by_name(elf, ".symtab");
 771         if (!symtab) {
 772                 WARN("can't find .symtab");
 773                 return NULL;
 774         }
 775
 776         s = elf_getscn(elf->elf, symtab->idx);
 777         if (!s) {
 778                 WARN_ELF("elf_getscn");
 779                 return NULL;
 780         }
 781
 782         data = elf_newdata(s);
 783         if (!data) {
 784                 WARN_ELF("elf_newdata");
 785                 return NULL;
 786         }
 787
 788         data->d_buf = &sym->sym;
 789         data->d_size = sizeof(sym->sym);
 790         data->d_align = 1;
 791         data->d_type = ELF_T_SYM;
 792
 793         sym->idx = symtab->sh.sh_size / sizeof(sym->sym);
 794
 795         symtab->sh.sh_size += data->d_size;
 796         symtab->changed = true;
 797
 798         symtab_shndx = find_section_by_name(elf, ".symtab_shndx");
 799         if (symtab_shndx) {
 800                 s = elf_getscn(elf->elf, symtab_shndx->idx);
 801                 if (!s) {
 802                         WARN_ELF("elf_getscn");
 803                         return NULL;
 804                 }
 805
 806                 data = elf_newdata(s);
 807                 if (!data) {
 808                         WARN_ELF("elf_newdata");
 809                         return NULL;
 810                 }
 811
 812                 data->d_buf = &sym->sym.st_size; /* conveniently 0 */
 813                 data->d_size = sizeof(Elf32_Word);
 814                 data->d_align = 4;
 815                 data->d_type = ELF_T_WORD;
 816
 817                 symtab_shndx->sh.sh_size += 4;
 818                 symtab_shndx->changed = true;
 819         }
 820
 821         sym->sec = find_section_by_index(elf, 0);
 822
 823         elf_add_symbol(elf, sym);
 824
 825         return sym;
 826 }
 827
 828 struct section *elf_create_section(struct elf *elf, const char *name,
 829                                    unsigned int sh_flags, size_t entsize, int nr)
 830 {
 831         struct section *sec, *shstrtab;
 832         size_t size = entsize * nr;
 833         Elf_Scn *s;
 834
 835         sec = malloc(sizeof(*sec));
 836         if (!sec) {
 837                 perror("malloc");
 838                 return NULL;
 839         }
 840         memset(sec, 0, sizeof(*sec));
 841
 842         INIT_LIST_HEAD(&sec->symbol_list);
 843         INIT_LIST_HEAD(&sec->reloc_list);
 844
 845         s = elf_newscn(elf->elf);
 846         if (!s) {
 847                 WARN_ELF("elf_newscn");
 848                 return NULL;
 849         }
 850
 851         sec->name = strdup(name);
 852         if (!sec->name) {
 853                 perror("strdup");
 854                 return NULL;
 855         }
 856
 857         sec->idx = elf_ndxscn(s);
 858         sec->changed = true;
 859
 860         sec->data = elf_newdata(s);
 861         if (!sec->data) {
 862                 WARN_ELF("elf_newdata");
 863                 return NULL;
 864         }
 865
 866         sec->data->d_size = size;
 867         sec->data->d_align = 1;
 868
 869         if (size) {
 870                 sec->data->d_buf = malloc(size);
 871                 if (!sec->data->d_buf) {
 872                         perror("malloc");
 873                         return NULL;
 874                 }
 875                 memset(sec->data->d_buf, 0, size);
 876         }
 877
 878         if (!gelf_getshdr(s, &sec->sh)) {
 879                 WARN_ELF("gelf_getshdr");
 880                 return NULL;
 881         }
 882
 883         sec->sh.sh_size = size;
 884         sec->sh.sh_entsize = entsize;
 885         sec->sh.sh_type = SHT_PROGBITS;
 886         sec->sh.sh_addralign = 1;
 887         sec->sh.sh_flags = SHF_ALLOC | sh_flags;
 888
 889         /* Add section name to .shstrtab (or .strtab for Clang) */
 890         shstrtab = find_section_by_name(elf, ".shstrtab");
 891         if (!shstrtab)
 892                 shstrtab = find_section_by_name(elf, ".strtab");
 893         if (!shstrtab) {
 894                 WARN("can't find .shstrtab or .strtab section");
 895                 return NULL;
 896         }
 897         sec->sh.sh_name = elf_add_string(elf, shstrtab, sec->name);
 898         if (sec->sh.sh_name == -1)
 899                 return NULL;
 900
 901         list_add_tail(&sec->list, &elf->sections);
 902         elf_hash_add(section, &sec->hash, sec->idx);
 903         elf_hash_add(section_name, &sec->name_hash, str_hash(sec->name));
 904
 905         elf->changed = true;
 906
 907         return sec;
 908 }
 909
 910 static struct section *elf_create_rel_reloc_section(struct elf *elf, struct section *base)
 911 {
 912         char *relocname;
 913         struct section *sec;
 914
 915         relocname = malloc(strlen(base->name) + strlen(".rel") + 1);
 916         if (!relocname) {
 917                 perror("malloc");
 918                 return NULL;
 919         }
 920         strcpy(relocname, ".rel");
 921         strcat(relocname, base->name);
 922
 923         sec = elf_create_section(elf, relocname, 0, sizeof(GElf_Rel), 0);
 924         free(relocname);
 925         if (!sec)
 926                 return NULL;
 927
 928         base->reloc = sec;
 929         sec->base = base;
 930
 931         sec->sh.sh_type = SHT_REL;
 932         sec->sh.sh_addralign = 8;
 933         sec->sh.sh_link = find_section_by_name(elf, ".symtab")->idx;
 934         sec->sh.sh_info = base->idx;
 935         sec->sh.sh_flags = SHF_INFO_LINK;
 936
 937         return sec;
 938 }
 939
 940 static struct section *elf_create_rela_reloc_section(struct elf *elf, struct section *base)
 941 {
 942         char *relocname;
 943         struct section *sec;
 944
 945         relocname = malloc(strlen(base->name) + strlen(".rela") + 1);
 946         if (!relocname) {
 947                 perror("malloc");
 948                 return NULL;
 949         }
 950         strcpy(relocname, ".rela");
 951         strcat(relocname, base->name);
 952
 953         sec = elf_create_section(elf, relocname, 0, sizeof(GElf_Rela), 0);
 954         free(relocname);
 955         if (!sec)
 956                 return NULL;
 957
 958         base->reloc = sec;
 959         sec->base = base;
 960
 961         sec->sh.sh_type = SHT_RELA;
 962         sec->sh.sh_addralign = 8;
 963         sec->sh.sh_link = find_section_by_name(elf, ".symtab")->idx;
 964         sec->sh.sh_info = base->idx;
 965         sec->sh.sh_flags = SHF_INFO_LINK;
 966
 967         return sec;
 968 }
 969
 970 static struct section *elf_create_reloc_section(struct elf *elf,
 971                                          struct section *base,
 972                                          int reltype)
 973 {
 974         switch (reltype) {
 975         case SHT_REL:  return elf_create_rel_reloc_section(elf, base);
 976         case SHT_RELA: return elf_create_rela_reloc_section(elf, base);
 977         default:       return NULL;
 978         }
 979 }
 980
 981 static int elf_rebuild_rel_reloc_section(struct section *sec)
 982 {
 983         struct reloc *reloc;
 984         int idx = 0;
 985         void *buf;
 986
 987         /* Allocate a buffer for relocations */
 988         buf = malloc(sec->sh.sh_size);
 989         if (!buf) {
 990                 perror("malloc");
 991                 return -1;
 992         }
 993
 994         sec->data->d_buf = buf;
 995         sec->data->d_size = sec->sh.sh_size;
 996         sec->data->d_type = ELF_T_REL;
 997
 998         idx = 0;
 999         list_for_each_entry(reloc, &sec->reloc_list, list) {
1000                 reloc->rel.r_offset = reloc->offset;
1001                 reloc->rel.r_info = GELF_R_INFO(reloc->sym->idx, reloc->type);
1002                 if (!gelf_update_rel(sec->data, idx, &reloc->rel)) {
1003                         WARN_ELF("gelf_update_rel");
1004                         return -1;
1005                 }
1006                 idx++;
1007         }
1008
1009         return 0;
1010 }
1011
1012 static int elf_rebuild_rela_reloc_section(struct section *sec)
1013 {
1014         struct reloc *reloc;
1015         int idx = 0;
1016         void *buf;
1017
1018         /* Allocate a buffer for relocations with addends */
1019         buf = malloc(sec->sh.sh_size);
1020         if (!buf) {
1021                 perror("malloc");
1022                 return -1;
1023         }
1024
1025         sec->data->d_buf = buf;
1026         sec->data->d_size = sec->sh.sh_size;
1027         sec->data->d_type = ELF_T_RELA;
1028
1029         idx = 0;
1030         list_for_each_entry(reloc, &sec->reloc_list, list) {
1031                 reloc->rela.r_offset = reloc->offset;
1032                 reloc->rela.r_addend = reloc->addend;
1033                 reloc->rela.r_info = GELF_R_INFO(reloc->sym->idx, reloc->type);
1034                 if (!gelf_update_rela(sec->data, idx, &reloc->rela)) {
1035                         WARN_ELF("gelf_update_rela");
1036                         return -1;
1037                 }
1038                 idx++;
1039         }
1040
1041         return 0;
1042 }
1043
1044 static int elf_rebuild_reloc_section(struct elf *elf, struct section *sec)
1045 {
1046         switch (sec->sh.sh_type) {
1047         case SHT_REL:  return elf_rebuild_rel_reloc_section(sec);
1048         case SHT_RELA: return elf_rebuild_rela_reloc_section(sec);
1049         default:       return -1;
1050         }
1051 }
1052
1053 int elf_write_insn(struct elf *elf, struct section *sec,
1054                    unsigned long offset, unsigned int len,
1055                    const char *insn)
1056 {
1057         Elf_Data *data = sec->data;
1058
1059         if (data->d_type != ELF_T_BYTE || data->d_off) {
1060                 WARN("write to unexpected data for section: %s", sec->name);
1061                 return -1;
1062         }
1063
1064         memcpy(data->d_buf + offset, insn, len);
1065         elf_flagdata(data, ELF_C_SET, ELF_F_DIRTY);
1066
1067         elf->changed = true;
1068
1069         return 0;
1070 }
1071
1072 int elf_write_reloc(struct elf *elf, struct reloc *reloc)
1073 {
1074         struct section *sec = reloc->sec;
1075
1076         if (sec->sh.sh_type == SHT_REL) {
1077                 reloc->rel.r_info = GELF_R_INFO(reloc->sym->idx, reloc->type);
1078                 reloc->rel.r_offset = reloc->offset;
1079
1080                 if (!gelf_update_rel(sec->data, reloc->idx, &reloc->rel)) {
1081                         WARN_ELF("gelf_update_rel");
1082                         return -1;
1083                 }
1084         } else {
1085                 reloc->rela.r_info = GELF_R_INFO(reloc->sym->idx, reloc->type);
1086                 reloc->rela.r_addend = reloc->addend;
1087                 reloc->rela.r_offset = reloc->offset;
1088
1089                 if (!gelf_update_rela(sec->data, reloc->idx, &reloc->rela)) {
1090                         WARN_ELF("gelf_update_rela");
1091                         return -1;
1092                 }
1093         }
1094
1095         elf->changed = true;
1096
1097         return 0;
1098 }
1099
1100 int elf_write(struct elf *elf)
1101 {
1102         struct section *sec;
1103         Elf_Scn *s;
1104
1105         /* Update changed relocation sections and section headers: */
1106         list_for_each_entry(sec, &elf->sections, list) {
1107                 if (sec->changed) {
1108                         s = elf_getscn(elf->elf, sec->idx);
1109                         if (!s) {
1110                                 WARN_ELF("elf_getscn");
1111                                 return -1;
1112                         }
1113                         if (!gelf_update_shdr(s, &sec->sh)) {
1114                                 WARN_ELF("gelf_update_shdr");
1115                                 return -1;
1116                         }
1117
1118                         if (sec->base &&
1119                             elf_rebuild_reloc_section(elf, sec)) {
1120                                 WARN("elf_rebuild_reloc_section");
1121                                 return -1;
1122                         }
1123
1124                         sec->changed = false;
1125                         elf->changed = true;
1126                 }
1127         }
1128
1129         /* Make sure the new section header entries get updated properly. */
1130         elf_flagelf(elf->elf, ELF_C_SET, ELF_F_DIRTY);
1131
1132         /* Write all changes to the file. */
1133         if (elf_update(elf->elf, ELF_C_WRITE) < 0) {
1134                 WARN_ELF("elf_update");
1135                 return -1;
1136         }
1137
1138         elf->changed = false;
1139
1140         return 0;
1141 }
1142
1143 void elf_close(struct elf *elf)
1144 {
1145         struct section *sec, *tmpsec;
1146         struct symbol *sym, *tmpsym;
1147         struct reloc *reloc, *tmpreloc;
1148
1149         if (elf->elf)
1150                 elf_end(elf->elf);
1151
1152         if (elf->fd > 0)
1153                 close(elf->fd);
1154
1155         list_for_each_entry_safe(sec, tmpsec, &elf->sections, list) {
1156                 list_for_each_entry_safe(sym, tmpsym, &sec->symbol_list, list) {
1157                         list_del(&sym->list);
1158                         hash_del(&sym->hash);
1159                         free(sym);
1160                 }
1161                 list_for_each_entry_safe(reloc, tmpreloc, &sec->reloc_list, list) {
1162                         list_del(&reloc->list);
1163                         hash_del(&reloc->hash);
1164                         free(reloc);
1165                 }
1166                 list_del(&sec->list);
1167                 free(sec);
1168         }
1169
1170         free(elf);
1171 }