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 (opts.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         INIT_LIST_HEAD(&sym->pv_target);
 378         sym->alias = sym;
 379
 380         sym->type = GELF_ST_TYPE(sym->sym.st_info);
 381         sym->bind = GELF_ST_BIND(sym->sym.st_info);
 382
 383         if (sym->type == STT_FILE)
 384                 elf->num_files++;
 385
 386         sym->offset = sym->sym.st_value;
 387         sym->len = sym->sym.st_size;
 388
 389         rb_add(&sym->node, &sym->sec->symbol_tree, symbol_to_offset);
 390         pnode = rb_prev(&sym->node);
 391         if (pnode)
 392                 entry = &rb_entry(pnode, struct symbol, node)->list;
 393         else
 394                 entry = &sym->sec->symbol_list;
 395         list_add(&sym->list, entry);
 396         elf_hash_add(symbol, &sym->hash, sym->idx);
 397         elf_hash_add(symbol_name, &sym->name_hash, str_hash(sym->name));
 398
 399         /*
 400          * Don't store empty STT_NOTYPE symbols in the rbtree.  They
 401          * can exist within a function, confusing the sorting.
 402          */
 403         if (!sym->len)
 404                 rb_erase(&sym->node, &sym->sec->symbol_tree);
 405 }
 406
 407 static int read_symbols(struct elf *elf)
 408 {
 409         struct section *symtab, *symtab_shndx, *sec;
 410         struct symbol *sym, *pfunc;
 411         int symbols_nr, i;
 412         char *coldstr;
 413         Elf_Data *shndx_data = NULL;
 414         Elf32_Word shndx;
 415
 416         symtab = find_section_by_name(elf, ".symtab");
 417         if (symtab) {
 418                 symtab_shndx = find_section_by_name(elf, ".symtab_shndx");
 419                 if (symtab_shndx)
 420                         shndx_data = symtab_shndx->data;
 421
 422                 symbols_nr = symtab->sh.sh_size / symtab->sh.sh_entsize;
 423         } else {
 424                 /*
 425                  * A missing symbol table is actually possible if it's an empty
 426                  * .o file. This can happen for thunk_64.o. Make sure to at
 427                  * least allocate the symbol hash tables so we can do symbol
 428                  * lookups without crashing.
 429                  */
 430                 symbols_nr = 0;
 431         }
 432
 433         if (!elf_alloc_hash(symbol, symbols_nr) ||
 434             !elf_alloc_hash(symbol_name, symbols_nr))
 435                 return -1;
 436
 437         for (i = 0; i < symbols_nr; i++) {
 438                 sym = malloc(sizeof(*sym));
 439                 if (!sym) {
 440                         perror("malloc");
 441                         return -1;
 442                 }
 443                 memset(sym, 0, sizeof(*sym));
 444
 445                 sym->idx = i;
 446
 447                 if (!gelf_getsymshndx(symtab->data, shndx_data, i, &sym->sym,
 448                                       &shndx)) {
 449                         WARN_ELF("gelf_getsymshndx");
 450                         goto err;
 451                 }
 452
 453                 sym->name = elf_strptr(elf->elf, symtab->sh.sh_link,
 454                                        sym->sym.st_name);
 455                 if (!sym->name) {
 456                         WARN_ELF("elf_strptr");
 457                         goto err;
 458                 }
 459
 460                 if ((sym->sym.st_shndx > SHN_UNDEF &&
 461                      sym->sym.st_shndx < SHN_LORESERVE) ||
 462                     (shndx_data && sym->sym.st_shndx == SHN_XINDEX)) {
 463                         if (sym->sym.st_shndx != SHN_XINDEX)
 464                                 shndx = sym->sym.st_shndx;
 465
 466                         sym->sec = find_section_by_index(elf, shndx);
 467                         if (!sym->sec) {
 468                                 WARN("couldn't find section for symbol %s",
 469                                      sym->name);
 470                                 goto err;
 471                         }
 472                         if (GELF_ST_TYPE(sym->sym.st_info) == STT_SECTION) {
 473                                 sym->name = sym->sec->name;
 474                                 sym->sec->sym = sym;
 475                         }
 476                 } else
 477                         sym->sec = find_section_by_index(elf, 0);
 478
 479                 elf_add_symbol(elf, sym);
 480         }
 481
 482         if (opts.stats) {
 483                 printf("nr_symbols: %lu\n", (unsigned long)symbols_nr);
 484                 printf("symbol_bits: %d\n", elf->symbol_bits);
 485         }
 486
 487         /* Create parent/child links for any cold subfunctions */
 488         list_for_each_entry(sec, &elf->sections, list) {
 489                 list_for_each_entry(sym, &sec->symbol_list, list) {
 490                         char pname[MAX_NAME_LEN + 1];
 491                         size_t pnamelen;
 492                         if (sym->type != STT_FUNC)
 493                                 continue;
 494
 495                         if (sym->pfunc == NULL)
 496                                 sym->pfunc = sym;
 497
 498                         if (sym->cfunc == NULL)
 499                                 sym->cfunc = sym;
 500
 501                         coldstr = strstr(sym->name, ".cold");
 502                         if (!coldstr)
 503                                 continue;
 504
 505                         pnamelen = coldstr - sym->name;
 506                         if (pnamelen > MAX_NAME_LEN) {
 507                                 WARN("%s(): parent function name exceeds maximum length of %d characters",
 508                                      sym->name, MAX_NAME_LEN);
 509                                 return -1;
 510                         }
 511
 512                         strncpy(pname, sym->name, pnamelen);
 513                         pname[pnamelen] = '\0';
 514                         pfunc = find_symbol_by_name(elf, pname);
 515
 516                         if (!pfunc) {
 517                                 WARN("%s(): can't find parent function",
 518                                      sym->name);
 519                                 return -1;
 520                         }
 521
 522                         sym->pfunc = pfunc;
 523                         pfunc->cfunc = sym;
 524
 525                         /*
 526                          * Unfortunately, -fnoreorder-functions puts the child
 527                          * inside the parent.  Remove the overlap so we can
 528                          * have sane assumptions.
 529                          *
 530                          * Note that pfunc->len now no longer matches
 531                          * pfunc->sym.st_size.
 532                          */
 533                         if (sym->sec == pfunc->sec &&
 534                             sym->offset >= pfunc->offset &&
 535                             sym->offset + sym->len == pfunc->offset + pfunc->len) {
 536                                 pfunc->len -= sym->len;
 537                         }
 538                 }
 539         }
 540
 541         return 0;
 542
 543 err:
 544         free(sym);
 545         return -1;
 546 }
 547
 548 static struct section *elf_create_reloc_section(struct elf *elf,
 549                                                 struct section *base,
 550                                                 int reltype);
 551
 552 int elf_add_reloc(struct elf *elf, struct section *sec, unsigned long offset,
 553                   unsigned int type, struct symbol *sym, s64 addend)
 554 {
 555         struct reloc *reloc;
 556
 557         if (!sec->reloc && !elf_create_reloc_section(elf, sec, SHT_RELA))
 558                 return -1;
 559
 560         reloc = malloc(sizeof(*reloc));
 561         if (!reloc) {
 562                 perror("malloc");
 563                 return -1;
 564         }
 565         memset(reloc, 0, sizeof(*reloc));
 566
 567         reloc->sec = sec->reloc;
 568         reloc->offset = offset;
 569         reloc->type = type;
 570         reloc->sym = sym;
 571         reloc->addend = addend;
 572
 573         list_add_tail(&reloc->list, &sec->reloc->reloc_list);
 574         elf_hash_add(reloc, &reloc->hash, reloc_hash(reloc));
 575
 576         sec->reloc->sh.sh_size += sec->reloc->sh.sh_entsize;
 577         sec->reloc->changed = true;
 578
 579         return 0;
 580 }
 581
 582 /*
 583  * Ensure that any reloc section containing references to @sym is marked
 584  * changed such that it will get re-generated in elf_rebuild_reloc_sections()
 585  * with the new symbol index.
 586  */
 587 static void elf_dirty_reloc_sym(struct elf *elf, struct symbol *sym)
 588 {
 589         struct section *sec;
 590
 591         list_for_each_entry(sec, &elf->sections, list) {
 592                 struct reloc *reloc;
 593
 594                 if (sec->changed)
 595                         continue;
 596
 597                 list_for_each_entry(reloc, &sec->reloc_list, list) {
 598                         if (reloc->sym == sym) {
 599                                 sec->changed = true;
 600                                 break;
 601                         }
 602                 }
 603         }
 604 }
 605
 606 /*
 607  * The libelf API is terrible; gelf_update_sym*() takes a data block relative
 608  * index value, *NOT* the symbol index. As such, iterate the data blocks and
 609  * adjust index until it fits.
 610  *
 611  * If no data block is found, allow adding a new data block provided the index
 612  * is only one past the end.
 613  */
 614 static int elf_update_symbol(struct elf *elf, struct section *symtab,
 615                              struct section *symtab_shndx, struct symbol *sym)
 616 {
 617         Elf32_Word shndx = sym->sec ? sym->sec->idx : SHN_UNDEF;
 618         Elf_Data *symtab_data = NULL, *shndx_data = NULL;
 619         Elf64_Xword entsize = symtab->sh.sh_entsize;
 620         int max_idx, idx = sym->idx;
 621         Elf_Scn *s, *t = NULL;
 622         bool is_special_shndx = sym->sym.st_shndx >= SHN_LORESERVE &&
 623                                 sym->sym.st_shndx != SHN_XINDEX;
 624
 625         if (is_special_shndx)
 626                 shndx = sym->sym.st_shndx;
 627
 628         s = elf_getscn(elf->elf, symtab->idx);
 629         if (!s) {
 630                 WARN_ELF("elf_getscn");
 631                 return -1;
 632         }
 633
 634         if (symtab_shndx) {
 635                 t = elf_getscn(elf->elf, symtab_shndx->idx);
 636                 if (!t) {
 637                         WARN_ELF("elf_getscn");
 638                         return -1;
 639                 }
 640         }
 641
 642         for (;;) {
 643                 /* get next data descriptor for the relevant sections */
 644                 symtab_data = elf_getdata(s, symtab_data);
 645                 if (t)
 646                         shndx_data = elf_getdata(t, shndx_data);
 647
 648                 /* end-of-list */
 649                 if (!symtab_data) {
 650                         void *buf;
 651
 652                         if (idx) {
 653                                 /* we don't do holes in symbol tables */
 654                                 WARN("index out of range");
 655                                 return -1;
 656                         }
 657
 658                         /* if @idx == 0, it's the next contiguous entry, create it */
 659                         symtab_data = elf_newdata(s);
 660                         if (t)
 661                                 shndx_data = elf_newdata(t);
 662
 663                         buf = calloc(1, entsize);
 664                         if (!buf) {
 665                                 WARN("malloc");
 666                                 return -1;
 667                         }
 668
 669                         symtab_data->d_buf = buf;
 670                         symtab_data->d_size = entsize;
 671                         symtab_data->d_align = 1;
 672                         symtab_data->d_type = ELF_T_SYM;
 673
 674                         symtab->sh.sh_size += entsize;
 675                         symtab->changed = true;
 676
 677                         if (t) {
 678                                 shndx_data->d_buf = &sym->sec->idx;
 679                                 shndx_data->d_size = sizeof(Elf32_Word);
 680                                 shndx_data->d_align = sizeof(Elf32_Word);
 681                                 shndx_data->d_type = ELF_T_WORD;
 682
 683                                 symtab_shndx->sh.sh_size += sizeof(Elf32_Word);
 684                                 symtab_shndx->changed = true;
 685                         }
 686
 687                         break;
 688                 }
 689
 690                 /* empty blocks should not happen */
 691                 if (!symtab_data->d_size) {
 692                         WARN("zero size data");
 693                         return -1;
 694                 }
 695
 696                 /* is this the right block? */
 697                 max_idx = symtab_data->d_size / entsize;
 698                 if (idx < max_idx)
 699                         break;
 700
 701                 /* adjust index and try again */
 702                 idx -= max_idx;
 703         }
 704
 705         /* something went side-ways */
 706         if (idx < 0) {
 707                 WARN("negative index");
 708                 return -1;
 709         }
 710
 711         /* setup extended section index magic and write the symbol */
 712         if ((shndx >= SHN_UNDEF && shndx < SHN_LORESERVE) || is_special_shndx) {
 713                 sym->sym.st_shndx = shndx;
 714                 if (!shndx_data)
 715                         shndx = 0;
 716         } else {
 717                 sym->sym.st_shndx = SHN_XINDEX;
 718                 if (!shndx_data) {
 719                         WARN("no .symtab_shndx");
 720                         return -1;
 721                 }
 722         }
 723
 724         if (!gelf_update_symshndx(symtab_data, shndx_data, idx, &sym->sym, shndx)) {
 725                 WARN_ELF("gelf_update_symshndx");
 726                 return -1;
 727         }
 728
 729         return 0;
 730 }
 731
 732 static struct symbol *
 733 elf_create_section_symbol(struct elf *elf, struct section *sec)
 734 {
 735         struct section *symtab, *symtab_shndx;
 736         Elf32_Word first_non_local, new_idx;
 737         struct symbol *sym, *old;
 738
 739         symtab = find_section_by_name(elf, ".symtab");
 740         if (symtab) {
 741                 symtab_shndx = find_section_by_name(elf, ".symtab_shndx");
 742         } else {
 743                 WARN("no .symtab");
 744                 return NULL;
 745         }
 746
 747         sym = calloc(1, sizeof(*sym));
 748         if (!sym) {
 749                 perror("malloc");
 750                 return NULL;
 751         }
 752
 753         sym->name = sec->name;
 754         sym->sec = sec;
 755
 756         // st_name 0
 757         sym->sym.st_info = GELF_ST_INFO(STB_LOCAL, STT_SECTION);
 758         // st_other 0
 759         // st_value 0
 760         // st_size 0
 761
 762         /*
 763          * Move the first global symbol, as per sh_info, into a new, higher
 764          * symbol index. This fees up a spot for a new local symbol.
 765          */
 766         first_non_local = symtab->sh.sh_info;
 767         new_idx = symtab->sh.sh_size / symtab->sh.sh_entsize;
 768         old = find_symbol_by_index(elf, first_non_local);
 769         if (old) {
 770                 old->idx = new_idx;
 771
 772                 hlist_del(&old->hash);
 773                 elf_hash_add(symbol, &old->hash, old->idx);
 774
 775                 elf_dirty_reloc_sym(elf, old);
 776
 777                 if (elf_update_symbol(elf, symtab, symtab_shndx, old)) {
 778                         WARN("elf_update_symbol move");
 779                         return NULL;
 780                 }
 781
 782                 new_idx = first_non_local;
 783         }
 784
 785         sym->idx = new_idx;
 786         if (elf_update_symbol(elf, symtab, symtab_shndx, sym)) {
 787                 WARN("elf_update_symbol");
 788                 return NULL;
 789         }
 790
 791         /*
 792          * Either way, we added a LOCAL symbol.
 793          */
 794         symtab->sh.sh_info += 1;
 795
 796         elf_add_symbol(elf, sym);
 797
 798         return sym;
 799 }
 800
 801 int elf_add_reloc_to_insn(struct elf *elf, struct section *sec,
 802                           unsigned long offset, unsigned int type,
 803                           struct section *insn_sec, unsigned long insn_off)
 804 {
 805         struct symbol *sym = insn_sec->sym;
 806         int addend = insn_off;
 807
 808         if (!sym) {
 809                 /*
 810                  * Due to how weak functions work, we must use section based
 811                  * relocations. Symbol based relocations would result in the
 812                  * weak and non-weak function annotations being overlaid on the
 813                  * non-weak function after linking.
 814                  */
 815                 sym = elf_create_section_symbol(elf, insn_sec);
 816                 if (!sym)
 817                         return -1;
 818
 819                 insn_sec->sym = sym;
 820         }
 821
 822         return elf_add_reloc(elf, sec, offset, type, sym, addend);
 823 }
 824
 825 static int read_rel_reloc(struct section *sec, int i, struct reloc *reloc, unsigned int *symndx)
 826 {
 827         if (!gelf_getrel(sec->data, i, &reloc->rel)) {
 828                 WARN_ELF("gelf_getrel");
 829                 return -1;
 830         }
 831         reloc->type = GELF_R_TYPE(reloc->rel.r_info);
 832         reloc->addend = 0;
 833         reloc->offset = reloc->rel.r_offset;
 834         *symndx = GELF_R_SYM(reloc->rel.r_info);
 835         return 0;
 836 }
 837
 838 static int read_rela_reloc(struct section *sec, int i, struct reloc *reloc, unsigned int *symndx)
 839 {
 840         if (!gelf_getrela(sec->data, i, &reloc->rela)) {
 841                 WARN_ELF("gelf_getrela");
 842                 return -1;
 843         }
 844         reloc->type = GELF_R_TYPE(reloc->rela.r_info);
 845         reloc->addend = reloc->rela.r_addend;
 846         reloc->offset = reloc->rela.r_offset;
 847         *symndx = GELF_R_SYM(reloc->rela.r_info);
 848         return 0;
 849 }
 850
 851 static int read_relocs(struct elf *elf)
 852 {
 853         struct section *sec;
 854         struct reloc *reloc;
 855         int i;
 856         unsigned int symndx;
 857         unsigned long nr_reloc, max_reloc = 0, tot_reloc = 0;
 858
 859         if (!elf_alloc_hash(reloc, elf->text_size / 16))
 860                 return -1;
 861
 862         list_for_each_entry(sec, &elf->sections, list) {
 863                 if ((sec->sh.sh_type != SHT_RELA) &&
 864                     (sec->sh.sh_type != SHT_REL))
 865                         continue;
 866
 867                 sec->base = find_section_by_index(elf, sec->sh.sh_info);
 868                 if (!sec->base) {
 869                         WARN("can't find base section for reloc section %s",
 870                              sec->name);
 871                         return -1;
 872                 }
 873
 874                 sec->base->reloc = sec;
 875
 876                 nr_reloc = 0;
 877                 for (i = 0; i < sec->sh.sh_size / sec->sh.sh_entsize; i++) {
 878                         reloc = malloc(sizeof(*reloc));
 879                         if (!reloc) {
 880                                 perror("malloc");
 881                                 return -1;
 882                         }
 883                         memset(reloc, 0, sizeof(*reloc));
 884                         switch (sec->sh.sh_type) {
 885                         case SHT_REL:
 886                                 if (read_rel_reloc(sec, i, reloc, &symndx))
 887                                         return -1;
 888                                 break;
 889                         case SHT_RELA:
 890                                 if (read_rela_reloc(sec, i, reloc, &symndx))
 891                                         return -1;
 892                                 break;
 893                         default: return -1;
 894                         }
 895
 896                         reloc->sec = sec;
 897                         reloc->idx = i;
 898                         reloc->sym = find_symbol_by_index(elf, symndx);
 899                         if (!reloc->sym) {
 900                                 WARN("can't find reloc entry symbol %d for %s",
 901                                      symndx, sec->name);
 902                                 return -1;
 903                         }
 904
 905                         list_add_tail(&reloc->list, &sec->reloc_list);
 906                         elf_hash_add(reloc, &reloc->hash, reloc_hash(reloc));
 907
 908                         nr_reloc++;
 909                 }
 910                 max_reloc = max(max_reloc, nr_reloc);
 911                 tot_reloc += nr_reloc;
 912         }
 913
 914         if (opts.stats) {
 915                 printf("max_reloc: %lu\n", max_reloc);
 916                 printf("tot_reloc: %lu\n", tot_reloc);
 917                 printf("reloc_bits: %d\n", elf->reloc_bits);
 918         }
 919
 920         return 0;
 921 }
 922
 923 struct elf *elf_open_read(const char *name, int flags)
 924 {
 925         struct elf *elf;
 926         Elf_Cmd cmd;
 927
 928         elf_version(EV_CURRENT);
 929
 930         elf = malloc(sizeof(*elf));
 931         if (!elf) {
 932                 perror("malloc");
 933                 return NULL;
 934         }
 935         memset(elf, 0, offsetof(struct elf, sections));
 936
 937         INIT_LIST_HEAD(&elf->sections);
 938
 939         elf->fd = open(name, flags);
 940         if (elf->fd == -1) {
 941                 fprintf(stderr, "objtool: Can't open '%s': %s\n",
 942                         name, strerror(errno));
 943                 goto err;
 944         }
 945
 946         if ((flags & O_ACCMODE) == O_RDONLY)
 947                 cmd = ELF_C_READ_MMAP;
 948         else if ((flags & O_ACCMODE) == O_RDWR)
 949                 cmd = ELF_C_RDWR;
 950         else /* O_WRONLY */
 951                 cmd = ELF_C_WRITE;
 952
 953         elf->elf = elf_begin(elf->fd, cmd, NULL);
 954         if (!elf->elf) {
 955                 WARN_ELF("elf_begin");
 956                 goto err;
 957         }
 958
 959         if (!gelf_getehdr(elf->elf, &elf->ehdr)) {
 960                 WARN_ELF("gelf_getehdr");
 961                 goto err;
 962         }
 963
 964         if (read_sections(elf))
 965                 goto err;
 966
 967         if (read_symbols(elf))
 968                 goto err;
 969
 970         if (read_relocs(elf))
 971                 goto err;
 972
 973         return elf;
 974
 975 err:
 976         elf_close(elf);
 977         return NULL;
 978 }
 979
 980 static int elf_add_string(struct elf *elf, struct section *strtab, char *str)
 981 {
 982         Elf_Data *data;
 983         Elf_Scn *s;
 984         int len;
 985
 986         if (!strtab)
 987                 strtab = find_section_by_name(elf, ".strtab");
 988         if (!strtab) {
 989                 WARN("can't find .strtab section");
 990                 return -1;
 991         }
 992
 993         s = elf_getscn(elf->elf, strtab->idx);
 994         if (!s) {
 995                 WARN_ELF("elf_getscn");
 996                 return -1;
 997         }
 998
 999         data = elf_newdata(s);
1000         if (!data) {
1001                 WARN_ELF("elf_newdata");
1002                 return -1;
1003         }
1004
1005         data->d_buf = str;
1006         data->d_size = strlen(str) + 1;
1007         data->d_align = 1;
1008
1009         len = strtab->sh.sh_size;
1010         strtab->sh.sh_size += data->d_size;
1011         strtab->changed = true;
1012
1013         return len;
1014 }
1015
1016 struct section *elf_create_section(struct elf *elf, const char *name,
1017                                    unsigned int sh_flags, size_t entsize, int nr)
1018 {
1019         struct section *sec, *shstrtab;
1020         size_t size = entsize * nr;
1021         Elf_Scn *s;
1022
1023         sec = malloc(sizeof(*sec));
1024         if (!sec) {
1025                 perror("malloc");
1026                 return NULL;
1027         }
1028         memset(sec, 0, sizeof(*sec));
1029
1030         INIT_LIST_HEAD(&sec->symbol_list);
1031         INIT_LIST_HEAD(&sec->reloc_list);
1032
1033         s = elf_newscn(elf->elf);
1034         if (!s) {
1035                 WARN_ELF("elf_newscn");
1036                 return NULL;
1037         }
1038
1039         sec->name = strdup(name);
1040         if (!sec->name) {
1041                 perror("strdup");
1042                 return NULL;
1043         }
1044
1045         sec->idx = elf_ndxscn(s);
1046         sec->changed = true;
1047
1048         sec->data = elf_newdata(s);
1049         if (!sec->data) {
1050                 WARN_ELF("elf_newdata");
1051                 return NULL;
1052         }
1053
1054         sec->data->d_size = size;
1055         sec->data->d_align = 1;
1056
1057         if (size) {
1058                 sec->data->d_buf = malloc(size);
1059                 if (!sec->data->d_buf) {
1060                         perror("malloc");
1061                         return NULL;
1062                 }
1063                 memset(sec->data->d_buf, 0, size);
1064         }
1065
1066         if (!gelf_getshdr(s, &sec->sh)) {
1067                 WARN_ELF("gelf_getshdr");
1068                 return NULL;
1069         }
1070
1071         sec->sh.sh_size = size;
1072         sec->sh.sh_entsize = entsize;
1073         sec->sh.sh_type = SHT_PROGBITS;
1074         sec->sh.sh_addralign = 1;
1075         sec->sh.sh_flags = SHF_ALLOC | sh_flags;
1076
1077         /* Add section name to .shstrtab (or .strtab for Clang) */
1078         shstrtab = find_section_by_name(elf, ".shstrtab");
1079         if (!shstrtab)
1080                 shstrtab = find_section_by_name(elf, ".strtab");
1081         if (!shstrtab) {
1082                 WARN("can't find .shstrtab or .strtab section");
1083                 return NULL;
1084         }
1085         sec->sh.sh_name = elf_add_string(elf, shstrtab, sec->name);
1086         if (sec->sh.sh_name == -1)
1087                 return NULL;
1088
1089         list_add_tail(&sec->list, &elf->sections);
1090         elf_hash_add(section, &sec->hash, sec->idx);
1091         elf_hash_add(section_name, &sec->name_hash, str_hash(sec->name));
1092
1093         elf->changed = true;
1094
1095         return sec;
1096 }
1097
1098 static struct section *elf_create_rel_reloc_section(struct elf *elf, struct section *base)
1099 {
1100         char *relocname;
1101         struct section *sec;
1102
1103         relocname = malloc(strlen(base->name) + strlen(".rel") + 1);
1104         if (!relocname) {
1105                 perror("malloc");
1106                 return NULL;
1107         }
1108         strcpy(relocname, ".rel");
1109         strcat(relocname, base->name);
1110
1111         sec = elf_create_section(elf, relocname, 0, sizeof(GElf_Rel), 0);
1112         free(relocname);
1113         if (!sec)
1114                 return NULL;
1115
1116         base->reloc = sec;
1117         sec->base = base;
1118
1119         sec->sh.sh_type = SHT_REL;
1120         sec->sh.sh_addralign = 8;
1121         sec->sh.sh_link = find_section_by_name(elf, ".symtab")->idx;
1122         sec->sh.sh_info = base->idx;
1123         sec->sh.sh_flags = SHF_INFO_LINK;
1124
1125         return sec;
1126 }
1127
1128 static struct section *elf_create_rela_reloc_section(struct elf *elf, struct section *base)
1129 {
1130         char *relocname;
1131         struct section *sec;
1132
1133         relocname = malloc(strlen(base->name) + strlen(".rela") + 1);
1134         if (!relocname) {
1135                 perror("malloc");
1136                 return NULL;
1137         }
1138         strcpy(relocname, ".rela");
1139         strcat(relocname, base->name);
1140
1141         sec = elf_create_section(elf, relocname, 0, sizeof(GElf_Rela), 0);
1142         free(relocname);
1143         if (!sec)
1144                 return NULL;
1145
1146         base->reloc = sec;
1147         sec->base = base;
1148
1149         sec->sh.sh_type = SHT_RELA;
1150         sec->sh.sh_addralign = 8;
1151         sec->sh.sh_link = find_section_by_name(elf, ".symtab")->idx;
1152         sec->sh.sh_info = base->idx;
1153         sec->sh.sh_flags = SHF_INFO_LINK;
1154
1155         return sec;
1156 }
1157
1158 static struct section *elf_create_reloc_section(struct elf *elf,
1159                                          struct section *base,
1160                                          int reltype)
1161 {
1162         switch (reltype) {
1163         case SHT_REL:  return elf_create_rel_reloc_section(elf, base);
1164         case SHT_RELA: return elf_create_rela_reloc_section(elf, base);
1165         default:       return NULL;
1166         }
1167 }
1168
1169 static int elf_rebuild_rel_reloc_section(struct section *sec)
1170 {
1171         struct reloc *reloc;
1172         int idx = 0;
1173         void *buf;
1174
1175         /* Allocate a buffer for relocations */
1176         buf = malloc(sec->sh.sh_size);
1177         if (!buf) {
1178                 perror("malloc");
1179                 return -1;
1180         }
1181
1182         sec->data->d_buf = buf;
1183         sec->data->d_size = sec->sh.sh_size;
1184         sec->data->d_type = ELF_T_REL;
1185
1186         idx = 0;
1187         list_for_each_entry(reloc, &sec->reloc_list, list) {
1188                 reloc->rel.r_offset = reloc->offset;
1189                 reloc->rel.r_info = GELF_R_INFO(reloc->sym->idx, reloc->type);
1190                 if (!gelf_update_rel(sec->data, idx, &reloc->rel)) {
1191                         WARN_ELF("gelf_update_rel");
1192                         return -1;
1193                 }
1194                 idx++;
1195         }
1196
1197         return 0;
1198 }
1199
1200 static int elf_rebuild_rela_reloc_section(struct section *sec)
1201 {
1202         struct reloc *reloc;
1203         int idx = 0;
1204         void *buf;
1205
1206         /* Allocate a buffer for relocations with addends */
1207         buf = malloc(sec->sh.sh_size);
1208         if (!buf) {
1209                 perror("malloc");
1210                 return -1;
1211         }
1212
1213         sec->data->d_buf = buf;
1214         sec->data->d_size = sec->sh.sh_size;
1215         sec->data->d_type = ELF_T_RELA;
1216
1217         idx = 0;
1218         list_for_each_entry(reloc, &sec->reloc_list, list) {
1219                 reloc->rela.r_offset = reloc->offset;
1220                 reloc->rela.r_addend = reloc->addend;
1221                 reloc->rela.r_info = GELF_R_INFO(reloc->sym->idx, reloc->type);
1222                 if (!gelf_update_rela(sec->data, idx, &reloc->rela)) {
1223                         WARN_ELF("gelf_update_rela");
1224                         return -1;
1225                 }
1226                 idx++;
1227         }
1228
1229         return 0;
1230 }
1231
1232 static int elf_rebuild_reloc_section(struct elf *elf, struct section *sec)
1233 {
1234         switch (sec->sh.sh_type) {
1235         case SHT_REL:  return elf_rebuild_rel_reloc_section(sec);
1236         case SHT_RELA: return elf_rebuild_rela_reloc_section(sec);
1237         default:       return -1;
1238         }
1239 }
1240
1241 int elf_write_insn(struct elf *elf, struct section *sec,
1242                    unsigned long offset, unsigned int len,
1243                    const char *insn)
1244 {
1245         Elf_Data *data = sec->data;
1246
1247         if (data->d_type != ELF_T_BYTE || data->d_off) {
1248                 WARN("write to unexpected data for section: %s", sec->name);
1249                 return -1;
1250         }
1251
1252         memcpy(data->d_buf + offset, insn, len);
1253         elf_flagdata(data, ELF_C_SET, ELF_F_DIRTY);
1254
1255         elf->changed = true;
1256
1257         return 0;
1258 }
1259
1260 int elf_write_reloc(struct elf *elf, struct reloc *reloc)
1261 {
1262         struct section *sec = reloc->sec;
1263
1264         if (sec->sh.sh_type == SHT_REL) {
1265                 reloc->rel.r_info = GELF_R_INFO(reloc->sym->idx, reloc->type);
1266                 reloc->rel.r_offset = reloc->offset;
1267
1268                 if (!gelf_update_rel(sec->data, reloc->idx, &reloc->rel)) {
1269                         WARN_ELF("gelf_update_rel");
1270                         return -1;
1271                 }
1272         } else {
1273                 reloc->rela.r_info = GELF_R_INFO(reloc->sym->idx, reloc->type);
1274                 reloc->rela.r_addend = reloc->addend;
1275                 reloc->rela.r_offset = reloc->offset;
1276
1277                 if (!gelf_update_rela(sec->data, reloc->idx, &reloc->rela)) {
1278                         WARN_ELF("gelf_update_rela");
1279                         return -1;
1280                 }
1281         }
1282
1283         elf->changed = true;
1284
1285         return 0;
1286 }
1287
1288 int elf_write(struct elf *elf)
1289 {
1290         struct section *sec;
1291         Elf_Scn *s;
1292
1293         if (opts.dryrun)
1294                 return 0;
1295
1296         /* Update changed relocation sections and section headers: */
1297         list_for_each_entry(sec, &elf->sections, list) {
1298                 if (sec->changed) {
1299                         s = elf_getscn(elf->elf, sec->idx);
1300                         if (!s) {
1301                                 WARN_ELF("elf_getscn");
1302                                 return -1;
1303                         }
1304                         if (!gelf_update_shdr(s, &sec->sh)) {
1305                                 WARN_ELF("gelf_update_shdr");
1306                                 return -1;
1307                         }
1308
1309                         if (sec->base &&
1310                             elf_rebuild_reloc_section(elf, sec)) {
1311                                 WARN("elf_rebuild_reloc_section");
1312                                 return -1;
1313                         }
1314
1315                         sec->changed = false;
1316                         elf->changed = true;
1317                 }
1318         }
1319
1320         /* Make sure the new section header entries get updated properly. */
1321         elf_flagelf(elf->elf, ELF_C_SET, ELF_F_DIRTY);
1322
1323         /* Write all changes to the file. */
1324         if (elf_update(elf->elf, ELF_C_WRITE) < 0) {
1325                 WARN_ELF("elf_update");
1326                 return -1;
1327         }
1328
1329         elf->changed = false;
1330
1331         return 0;
1332 }
1333
1334 void elf_close(struct elf *elf)
1335 {
1336         struct section *sec, *tmpsec;
1337         struct symbol *sym, *tmpsym;
1338         struct reloc *reloc, *tmpreloc;
1339
1340         if (elf->elf)
1341                 elf_end(elf->elf);
1342
1343         if (elf->fd > 0)
1344                 close(elf->fd);
1345
1346         list_for_each_entry_safe(sec, tmpsec, &elf->sections, list) {
1347                 list_for_each_entry_safe(sym, tmpsym, &sec->symbol_list, list) {
1348                         list_del(&sym->list);
1349                         hash_del(&sym->hash);
1350                         free(sym);
1351                 }
1352                 list_for_each_entry_safe(reloc, tmpreloc, &sec->reloc_list, list) {
1353                         list_del(&reloc->list);
1354                         hash_del(&reloc->hash);
1355                         free(reloc);
1356                 }
1357                 list_del(&sec->list);
1358                 free(sec);
1359         }
1360
1361         free(elf);
1362 }