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