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->changed = true;
 512
 513         return 0;
 514 }
 515
 516 int elf_add_reloc_to_insn(struct elf *elf, struct section *sec,
 517                           unsigned long offset, unsigned int type,
 518                           struct section *insn_sec, unsigned long insn_off)
 519 {
 520         struct symbol *sym;
 521         int addend;
 522
 523         if (insn_sec->sym) {
 524                 sym = insn_sec->sym;
 525                 addend = insn_off;
 526
 527         } else {
 528                 /*
 529                  * The Clang assembler strips section symbols, so we have to
 530                  * reference the function symbol instead:
 531                  */
 532                 sym = find_symbol_containing(insn_sec, insn_off);
 533                 if (!sym) {
 534                         /*
 535                          * Hack alert.  This happens when we need to reference
 536                          * the NOP pad insn immediately after the function.
 537                          */
 538                         sym = find_symbol_containing(insn_sec, insn_off - 1);
 539                 }
 540
 541                 if (!sym) {
 542                         WARN("can't find symbol containing %s+0x%lx", insn_sec->name, insn_off);
 543                         return -1;
 544                 }
 545
 546                 addend = insn_off - sym->offset;
 547         }
 548
 549         return elf_add_reloc(elf, sec, offset, type, sym, addend);
 550 }
 551
 552 static int read_rel_reloc(struct section *sec, int i, struct reloc *reloc, unsigned int *symndx)
 553 {
 554         if (!gelf_getrel(sec->data, i, &reloc->rel)) {
 555                 WARN_ELF("gelf_getrel");
 556                 return -1;
 557         }
 558         reloc->type = GELF_R_TYPE(reloc->rel.r_info);
 559         reloc->addend = 0;
 560         reloc->offset = reloc->rel.r_offset;
 561         *symndx = GELF_R_SYM(reloc->rel.r_info);
 562         return 0;
 563 }
 564
 565 static int read_rela_reloc(struct section *sec, int i, struct reloc *reloc, unsigned int *symndx)
 566 {
 567         if (!gelf_getrela(sec->data, i, &reloc->rela)) {
 568                 WARN_ELF("gelf_getrela");
 569                 return -1;
 570         }
 571         reloc->type = GELF_R_TYPE(reloc->rela.r_info);
 572         reloc->addend = reloc->rela.r_addend;
 573         reloc->offset = reloc->rela.r_offset;
 574         *symndx = GELF_R_SYM(reloc->rela.r_info);
 575         return 0;
 576 }
 577
 578 static int read_relocs(struct elf *elf)
 579 {
 580         struct section *sec;
 581         struct reloc *reloc;
 582         int i;
 583         unsigned int symndx;
 584         unsigned long nr_reloc, max_reloc = 0, tot_reloc = 0;
 585
 586         if (!elf_alloc_hash(reloc, elf->text_size / 16))
 587                 return -1;
 588
 589         list_for_each_entry(sec, &elf->sections, list) {
 590                 if ((sec->sh.sh_type != SHT_RELA) &&
 591                     (sec->sh.sh_type != SHT_REL))
 592                         continue;
 593
 594                 sec->base = find_section_by_index(elf, sec->sh.sh_info);
 595                 if (!sec->base) {
 596                         WARN("can't find base section for reloc section %s",
 597                              sec->name);
 598                         return -1;
 599                 }
 600
 601                 sec->base->reloc = sec;
 602
 603                 nr_reloc = 0;
 604                 for (i = 0; i < sec->sh.sh_size / sec->sh.sh_entsize; i++) {
 605                         reloc = malloc(sizeof(*reloc));
 606                         if (!reloc) {
 607                                 perror("malloc");
 608                                 return -1;
 609                         }
 610                         memset(reloc, 0, sizeof(*reloc));
 611                         switch (sec->sh.sh_type) {
 612                         case SHT_REL:
 613                                 if (read_rel_reloc(sec, i, reloc, &symndx))
 614                                         return -1;
 615                                 break;
 616                         case SHT_RELA:
 617                                 if (read_rela_reloc(sec, i, reloc, &symndx))
 618                                         return -1;
 619                                 break;
 620                         default: return -1;
 621                         }
 622
 623                         reloc->sec = sec;
 624                         reloc->idx = i;
 625                         reloc->sym = find_symbol_by_index(elf, symndx);
 626                         if (!reloc->sym) {
 627                                 WARN("can't find reloc entry symbol %d for %s",
 628                                      symndx, sec->name);
 629                                 return -1;
 630                         }
 631
 632                         list_add_tail(&reloc->list, &sec->reloc_list);
 633                         elf_hash_add(reloc, &reloc->hash, reloc_hash(reloc));
 634
 635                         nr_reloc++;
 636                 }
 637                 max_reloc = max(max_reloc, nr_reloc);
 638                 tot_reloc += nr_reloc;
 639         }
 640
 641         if (stats) {
 642                 printf("max_reloc: %lu\n", max_reloc);
 643                 printf("tot_reloc: %lu\n", tot_reloc);
 644                 printf("reloc_bits: %d\n", elf->reloc_bits);
 645         }
 646
 647         return 0;
 648 }
 649
 650 struct elf *elf_open_read(const char *name, int flags)
 651 {
 652         struct elf *elf;
 653         Elf_Cmd cmd;
 654
 655         elf_version(EV_CURRENT);
 656
 657         elf = malloc(sizeof(*elf));
 658         if (!elf) {
 659                 perror("malloc");
 660                 return NULL;
 661         }
 662         memset(elf, 0, offsetof(struct elf, sections));
 663
 664         INIT_LIST_HEAD(&elf->sections);
 665
 666         elf->fd = open(name, flags);
 667         if (elf->fd == -1) {
 668                 fprintf(stderr, "objtool: Can't open '%s': %s\n",
 669                         name, strerror(errno));
 670                 goto err;
 671         }
 672
 673         if ((flags & O_ACCMODE) == O_RDONLY)
 674                 cmd = ELF_C_READ_MMAP;
 675         else if ((flags & O_ACCMODE) == O_RDWR)
 676                 cmd = ELF_C_RDWR;
 677         else /* O_WRONLY */
 678                 cmd = ELF_C_WRITE;
 679
 680         elf->elf = elf_begin(elf->fd, cmd, NULL);
 681         if (!elf->elf) {
 682                 WARN_ELF("elf_begin");
 683                 goto err;
 684         }
 685
 686         if (!gelf_getehdr(elf->elf, &elf->ehdr)) {
 687                 WARN_ELF("gelf_getehdr");
 688                 goto err;
 689         }
 690
 691         if (read_sections(elf))
 692                 goto err;
 693
 694         if (read_symbols(elf))
 695                 goto err;
 696
 697         if (read_relocs(elf))
 698                 goto err;
 699
 700         return elf;
 701
 702 err:
 703         elf_close(elf);
 704         return NULL;
 705 }
 706
 707 static int elf_add_string(struct elf *elf, struct section *strtab, char *str)
 708 {
 709         Elf_Data *data;
 710         Elf_Scn *s;
 711         int len;
 712
 713         if (!strtab)
 714                 strtab = find_section_by_name(elf, ".strtab");
 715         if (!strtab) {
 716                 WARN("can't find .strtab section");
 717                 return -1;
 718         }
 719
 720         s = elf_getscn(elf->elf, strtab->idx);
 721         if (!s) {
 722                 WARN_ELF("elf_getscn");
 723                 return -1;
 724         }
 725
 726         data = elf_newdata(s);
 727         if (!data) {
 728                 WARN_ELF("elf_newdata");
 729                 return -1;
 730         }
 731
 732         data->d_buf = str;
 733         data->d_size = strlen(str) + 1;
 734         data->d_align = 1;
 735
 736         len = strtab->sh.sh_size;
 737         strtab->sh.sh_size += data->d_size;
 738         strtab->changed = true;
 739
 740         return len;
 741 }
 742
 743 struct symbol *elf_create_undef_symbol(struct elf *elf, const char *name)
 744 {
 745         struct section *symtab, *symtab_shndx;
 746         struct symbol *sym;
 747         Elf_Data *data;
 748         Elf_Scn *s;
 749
 750         sym = malloc(sizeof(*sym));
 751         if (!sym) {
 752                 perror("malloc");
 753                 return NULL;
 754         }
 755         memset(sym, 0, sizeof(*sym));
 756
 757         sym->name = strdup(name);
 758
 759         sym->sym.st_name = elf_add_string(elf, NULL, sym->name);
 760         if (sym->sym.st_name == -1)
 761                 return NULL;
 762
 763         sym->sym.st_info = GELF_ST_INFO(STB_GLOBAL, STT_NOTYPE);
 764         // st_other 0
 765         // st_shndx 0
 766         // st_value 0
 767         // st_size 0
 768
 769         symtab = find_section_by_name(elf, ".symtab");
 770         if (!symtab) {
 771                 WARN("can't find .symtab");
 772                 return NULL;
 773         }
 774
 775         s = elf_getscn(elf->elf, symtab->idx);
 776         if (!s) {
 777                 WARN_ELF("elf_getscn");
 778                 return NULL;
 779         }
 780
 781         data = elf_newdata(s);
 782         if (!data) {
 783                 WARN_ELF("elf_newdata");
 784                 return NULL;
 785         }
 786
 787         data->d_buf = &sym->sym;
 788         data->d_size = sizeof(sym->sym);
 789         data->d_align = 1;
 790         data->d_type = ELF_T_SYM;
 791
 792         sym->idx = symtab->sh.sh_size / sizeof(sym->sym);
 793
 794         symtab->sh.sh_size += data->d_size;
 795         symtab->changed = true;
 796
 797         symtab_shndx = find_section_by_name(elf, ".symtab_shndx");
 798         if (symtab_shndx) {
 799                 s = elf_getscn(elf->elf, symtab_shndx->idx);
 800                 if (!s) {
 801                         WARN_ELF("elf_getscn");
 802                         return NULL;
 803                 }
 804
 805                 data = elf_newdata(s);
 806                 if (!data) {
 807                         WARN_ELF("elf_newdata");
 808                         return NULL;
 809                 }
 810
 811                 data->d_buf = &sym->sym.st_size; /* conveniently 0 */
 812                 data->d_size = sizeof(Elf32_Word);
 813                 data->d_align = 4;
 814                 data->d_type = ELF_T_WORD;
 815
 816                 symtab_shndx->sh.sh_size += 4;
 817                 symtab_shndx->changed = true;
 818         }
 819
 820         sym->sec = find_section_by_index(elf, 0);
 821
 822         elf_add_symbol(elf, sym);
 823
 824         return sym;
 825 }
 826
 827 struct section *elf_create_section(struct elf *elf, const char *name,
 828                                    unsigned int sh_flags, size_t entsize, int nr)
 829 {
 830         struct section *sec, *shstrtab;
 831         size_t size = entsize * nr;
 832         Elf_Scn *s;
 833
 834         sec = malloc(sizeof(*sec));
 835         if (!sec) {
 836                 perror("malloc");
 837                 return NULL;
 838         }
 839         memset(sec, 0, sizeof(*sec));
 840
 841         INIT_LIST_HEAD(&sec->symbol_list);
 842         INIT_LIST_HEAD(&sec->reloc_list);
 843
 844         s = elf_newscn(elf->elf);
 845         if (!s) {
 846                 WARN_ELF("elf_newscn");
 847                 return NULL;
 848         }
 849
 850         sec->name = strdup(name);
 851         if (!sec->name) {
 852                 perror("strdup");
 853                 return NULL;
 854         }
 855
 856         sec->idx = elf_ndxscn(s);
 857         sec->changed = true;
 858
 859         sec->data = elf_newdata(s);
 860         if (!sec->data) {
 861                 WARN_ELF("elf_newdata");
 862                 return NULL;
 863         }
 864
 865         sec->data->d_size = size;
 866         sec->data->d_align = 1;
 867
 868         if (size) {
 869                 sec->data->d_buf = malloc(size);
 870                 if (!sec->data->d_buf) {
 871                         perror("malloc");
 872                         return NULL;
 873                 }
 874                 memset(sec->data->d_buf, 0, size);
 875         }
 876
 877         if (!gelf_getshdr(s, &sec->sh)) {
 878                 WARN_ELF("gelf_getshdr");
 879                 return NULL;
 880         }
 881
 882         sec->sh.sh_size = size;
 883         sec->sh.sh_entsize = entsize;
 884         sec->sh.sh_type = SHT_PROGBITS;
 885         sec->sh.sh_addralign = 1;
 886         sec->sh.sh_flags = SHF_ALLOC | sh_flags;
 887
 888         /* Add section name to .shstrtab (or .strtab for Clang) */
 889         shstrtab = find_section_by_name(elf, ".shstrtab");
 890         if (!shstrtab)
 891                 shstrtab = find_section_by_name(elf, ".strtab");
 892         if (!shstrtab) {
 893                 WARN("can't find .shstrtab or .strtab section");
 894                 return NULL;
 895         }
 896         sec->sh.sh_name = elf_add_string(elf, shstrtab, sec->name);
 897         if (sec->sh.sh_name == -1)
 898                 return NULL;
 899
 900         list_add_tail(&sec->list, &elf->sections);
 901         elf_hash_add(section, &sec->hash, sec->idx);
 902         elf_hash_add(section_name, &sec->name_hash, str_hash(sec->name));
 903
 904         elf->changed = true;
 905
 906         return sec;
 907 }
 908
 909 static struct section *elf_create_rel_reloc_section(struct elf *elf, struct section *base)
 910 {
 911         char *relocname;
 912         struct section *sec;
 913
 914         relocname = malloc(strlen(base->name) + strlen(".rel") + 1);
 915         if (!relocname) {
 916                 perror("malloc");
 917                 return NULL;
 918         }
 919         strcpy(relocname, ".rel");
 920         strcat(relocname, base->name);
 921
 922         sec = elf_create_section(elf, relocname, 0, sizeof(GElf_Rel), 0);
 923         free(relocname);
 924         if (!sec)
 925                 return NULL;
 926
 927         base->reloc = sec;
 928         sec->base = base;
 929
 930         sec->sh.sh_type = SHT_REL;
 931         sec->sh.sh_addralign = 8;
 932         sec->sh.sh_link = find_section_by_name(elf, ".symtab")->idx;
 933         sec->sh.sh_info = base->idx;
 934         sec->sh.sh_flags = SHF_INFO_LINK;
 935
 936         return sec;
 937 }
 938
 939 static struct section *elf_create_rela_reloc_section(struct elf *elf, struct section *base)
 940 {
 941         char *relocname;
 942         struct section *sec;
 943
 944         relocname = malloc(strlen(base->name) + strlen(".rela") + 1);
 945         if (!relocname) {
 946                 perror("malloc");
 947                 return NULL;
 948         }
 949         strcpy(relocname, ".rela");
 950         strcat(relocname, base->name);
 951
 952         sec = elf_create_section(elf, relocname, 0, sizeof(GElf_Rela), 0);
 953         free(relocname);
 954         if (!sec)
 955                 return NULL;
 956
 957         base->reloc = sec;
 958         sec->base = base;
 959
 960         sec->sh.sh_type = SHT_RELA;
 961         sec->sh.sh_addralign = 8;
 962         sec->sh.sh_link = find_section_by_name(elf, ".symtab")->idx;
 963         sec->sh.sh_info = base->idx;
 964         sec->sh.sh_flags = SHF_INFO_LINK;
 965
 966         return sec;
 967 }
 968
 969 static struct section *elf_create_reloc_section(struct elf *elf,
 970                                          struct section *base,
 971                                          int reltype)
 972 {
 973         switch (reltype) {
 974         case SHT_REL:  return elf_create_rel_reloc_section(elf, base);
 975         case SHT_RELA: return elf_create_rela_reloc_section(elf, base);
 976         default:       return NULL;
 977         }
 978 }
 979
 980 static int elf_rebuild_rel_reloc_section(struct section *sec, int nr)
 981 {
 982         struct reloc *reloc;
 983         int idx = 0, size;
 984         void *buf;
 985
 986         /* Allocate a buffer for relocations */
 987         size = nr * sizeof(GElf_Rel);
 988         buf = malloc(size);
 989         if (!buf) {
 990                 perror("malloc");
 991                 return -1;
 992         }
 993
 994         sec->data->d_buf = buf;
 995         sec->data->d_size = size;
 996         sec->data->d_type = ELF_T_REL;
 997
 998         sec->sh.sh_size = size;
 999
1000         idx = 0;
1001         list_for_each_entry(reloc, &sec->reloc_list, list) {
1002                 reloc->rel.r_offset = reloc->offset;
1003                 reloc->rel.r_info = GELF_R_INFO(reloc->sym->idx, reloc->type);
1004                 gelf_update_rel(sec->data, idx, &reloc->rel);
1005                 idx++;
1006         }
1007
1008         return 0;
1009 }
1010
1011 static int elf_rebuild_rela_reloc_section(struct section *sec, int nr)
1012 {
1013         struct reloc *reloc;
1014         int idx = 0, size;
1015         void *buf;
1016
1017         /* Allocate a buffer for relocations with addends */
1018         size = nr * sizeof(GElf_Rela);
1019         buf = malloc(size);
1020         if (!buf) {
1021                 perror("malloc");
1022                 return -1;
1023         }
1024
1025         sec->data->d_buf = buf;
1026         sec->data->d_size = size;
1027         sec->data->d_type = ELF_T_RELA;
1028
1029         sec->sh.sh_size = size;
1030
1031         idx = 0;
1032         list_for_each_entry(reloc, &sec->reloc_list, list) {
1033                 reloc->rela.r_offset = reloc->offset;
1034                 reloc->rela.r_addend = reloc->addend;
1035                 reloc->rela.r_info = GELF_R_INFO(reloc->sym->idx, reloc->type);
1036                 gelf_update_rela(sec->data, idx, &reloc->rela);
1037                 idx++;
1038         }
1039
1040         return 0;
1041 }
1042
1043 static int elf_rebuild_reloc_section(struct elf *elf, struct section *sec)
1044 {
1045         struct reloc *reloc;
1046         int nr;
1047
1048         nr = 0;
1049         list_for_each_entry(reloc, &sec->reloc_list, list)
1050                 nr++;
1051
1052         switch (sec->sh.sh_type) {
1053         case SHT_REL:  return elf_rebuild_rel_reloc_section(sec, nr);
1054         case SHT_RELA: return elf_rebuild_rela_reloc_section(sec, nr);
1055         default:       return -1;
1056         }
1057 }
1058
1059 int elf_write_insn(struct elf *elf, struct section *sec,
1060                    unsigned long offset, unsigned int len,
1061                    const char *insn)
1062 {
1063         Elf_Data *data = sec->data;
1064
1065         if (data->d_type != ELF_T_BYTE || data->d_off) {
1066                 WARN("write to unexpected data for section: %s", sec->name);
1067                 return -1;
1068         }
1069
1070         memcpy(data->d_buf + offset, insn, len);
1071         elf_flagdata(data, ELF_C_SET, ELF_F_DIRTY);
1072
1073         elf->changed = true;
1074
1075         return 0;
1076 }
1077
1078 int elf_write_reloc(struct elf *elf, struct reloc *reloc)
1079 {
1080         struct section *sec = reloc->sec;
1081
1082         if (sec->sh.sh_type == SHT_REL) {
1083                 reloc->rel.r_info = GELF_R_INFO(reloc->sym->idx, reloc->type);
1084                 reloc->rel.r_offset = reloc->offset;
1085
1086                 if (!gelf_update_rel(sec->data, reloc->idx, &reloc->rel)) {
1087                         WARN_ELF("gelf_update_rel");
1088                         return -1;
1089                 }
1090         } else {
1091                 reloc->rela.r_info = GELF_R_INFO(reloc->sym->idx, reloc->type);
1092                 reloc->rela.r_addend = reloc->addend;
1093                 reloc->rela.r_offset = reloc->offset;
1094
1095                 if (!gelf_update_rela(sec->data, reloc->idx, &reloc->rela)) {
1096                         WARN_ELF("gelf_update_rela");
1097                         return -1;
1098                 }
1099         }
1100
1101         elf->changed = true;
1102
1103         return 0;
1104 }
1105
1106 int elf_write(struct elf *elf)
1107 {
1108         struct section *sec;
1109         Elf_Scn *s;
1110
1111         /* Update changed relocation sections and section headers: */
1112         list_for_each_entry(sec, &elf->sections, list) {
1113                 if (sec->changed) {
1114                         if (sec->base &&
1115                             elf_rebuild_reloc_section(elf, sec)) {
1116                                 WARN("elf_rebuild_reloc_section");
1117                                 return -1;
1118                         }
1119
1120                         s = elf_getscn(elf->elf, sec->idx);
1121                         if (!s) {
1122                                 WARN_ELF("elf_getscn");
1123                                 return -1;
1124                         }
1125                         if (!gelf_update_shdr(s, &sec->sh)) {
1126                                 WARN_ELF("gelf_update_shdr");
1127                                 return -1;
1128                         }
1129
1130                         sec->changed = false;
1131                         elf->changed = true;
1132                 }
1133         }
1134
1135         /* Make sure the new section header entries get updated properly. */
1136         elf_flagelf(elf->elf, ELF_C_SET, ELF_F_DIRTY);
1137
1138         /* Write all changes to the file. */
1139         if (elf_update(elf->elf, ELF_C_WRITE) < 0) {
1140                 WARN_ELF("elf_update");
1141                 return -1;
1142         }
1143
1144         elf->changed = false;
1145
1146         return 0;
1147 }
1148
1149 void elf_close(struct elf *elf)
1150 {
1151         struct section *sec, *tmpsec;
1152         struct symbol *sym, *tmpsym;
1153         struct reloc *reloc, *tmpreloc;
1154
1155         if (elf->elf)
1156                 elf_end(elf->elf);
1157
1158         if (elf->fd > 0)
1159                 close(elf->fd);
1160
1161         list_for_each_entry_safe(sec, tmpsec, &elf->sections, list) {
1162                 list_for_each_entry_safe(sym, tmpsym, &sec->symbol_list, list) {
1163                         list_del(&sym->list);
1164                         hash_del(&sym->hash);
1165                         free(sym);
1166                 }
1167                 list_for_each_entry_safe(reloc, tmpreloc, &sec->reloc_list, list) {
1168                         list_del(&reloc->list);
1169                         hash_del(&reloc->hash);
1170                         free(reloc);
1171                 }
1172                 list_del(&sec->list);
1173                 free(sec);
1174         }
1175
1176         free(elf);
1177 }