tools/objtool/elf.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /*
   3  * elf.c - ELF access library
   4  *
   5  * Adapted from kpatch (https://github.com/dynup/kpatch):
   6  * Copyright (C) 2013-2015 Josh Poimboeuf <jpoimboe@redhat.com>
   7  * Copyright (C) 2014 Seth Jennings <sjenning@redhat.com>
   8  */
   9
  10 #include <sys/types.h>
  11 #include <sys/stat.h>
  12 #include <fcntl.h>
  13 #include <stdio.h>
  14 #include <stdlib.h>
  15 #include <string.h>
  16 #include <unistd.h>
  17 #include <errno.h>
  18 #include "builtin.h"
  19
  20 #include "elf.h"
  21 #include "warn.h"
  22
  23 #define MAX_NAME_LEN 128
  24
  25 static inline u32 str_hash(const char *str)
  26 {
  27         return jhash(str, strlen(str), 0);
  28 }
  29
  30 static inline int elf_hash_bits(void)
  31 {
  32         return vmlinux ? ELF_HASH_BITS : 16;
  33 }
  34
  35 #define elf_hash_add(hashtable, node, key) \
  36         hlist_add_head(node, &hashtable[hash_min(key, elf_hash_bits())])
  37
  38 static void elf_hash_init(struct hlist_head *table)
  39 {
  40         __hash_init(table, 1U << elf_hash_bits());
  41 }
  42
  43 #define elf_hash_for_each_possible(name, obj, member, key)                      \
  44         hlist_for_each_entry(obj, &name[hash_min(key, elf_hash_bits())], member)
  45
  46 static void rb_add(struct rb_root *tree, struct rb_node *node,
  47                    int (*cmp)(struct rb_node *, const struct rb_node *))
  48 {
  49         struct rb_node **link = &tree->rb_node;
  50         struct rb_node *parent = NULL;
  51
  52         while (*link) {
  53                 parent = *link;
  54                 if (cmp(node, parent) < 0)
  55                         link = &parent->rb_left;
  56                 else
  57                         link = &parent->rb_right;
  58         }
  59
  60         rb_link_node(node, parent, link);
  61         rb_insert_color(node, tree);
  62 }
  63
  64 static struct rb_node *rb_find_first(const struct rb_root *tree, const void *key,
  65                                int (*cmp)(const void *key, const struct rb_node *))
  66 {
  67         struct rb_node *node = tree->rb_node;
  68         struct rb_node *match = NULL;
  69
  70         while (node) {
  71                 int c = cmp(key, node);
  72                 if (c <= 0) {
  73                         if (!c)
  74                                 match = node;
  75                         node = node->rb_left;
  76                 } else if (c > 0) {
  77                         node = node->rb_right;
  78                 }
  79         }
  80
  81         return match;
  82 }
  83
  84 static struct rb_node *rb_next_match(struct rb_node *node, const void *key,
  85                                     int (*cmp)(const void *key, const struct rb_node *))
  86 {
  87         node = rb_next(node);
  88         if (node && cmp(key, node))
  89                 node = NULL;
  90         return node;
  91 }
  92
  93 #define rb_for_each(tree, node, key, cmp) \
  94         for ((node) = rb_find_first((tree), (key), (cmp)); \
  95              (node); (node) = rb_next_match((node), (key), (cmp)))
  96
  97 static int symbol_to_offset(struct rb_node *a, const struct rb_node *b)
  98 {
  99         struct symbol *sa = rb_entry(a, struct symbol, node);
 100         struct symbol *sb = rb_entry(b, struct symbol, node);
 101
 102         if (sa->offset < sb->offset)
 103                 return -1;
 104         if (sa->offset > sb->offset)
 105                 return 1;
 106
 107         if (sa->len < sb->len)
 108                 return -1;
 109         if (sa->len > sb->len)
 110                 return 1;
 111
 112         sa->alias = sb;
 113
 114         return 0;
 115 }
 116
 117 static int symbol_by_offset(const void *key, const struct rb_node *node)
 118 {
 119         const struct symbol *s = rb_entry(node, struct symbol, node);
 120         const unsigned long *o = key;
 121
 122         if (*o < s->offset)
 123                 return -1;
 124         if (*o >= s->offset + s->len)
 125                 return 1;
 126
 127         return 0;
 128 }
 129
 130 struct section *find_section_by_name(const struct elf *elf, const char *name)
 131 {
 132         struct section *sec;
 133
 134         elf_hash_for_each_possible(elf->section_name_hash, sec, name_hash, str_hash(name))
 135                 if (!strcmp(sec->name, name))
 136                         return sec;
 137
 138         return NULL;
 139 }
 140
 141 static struct section *find_section_by_index(struct elf *elf,
 142                                              unsigned int idx)
 143 {
 144         struct section *sec;
 145
 146         elf_hash_for_each_possible(elf->section_hash, sec, hash, idx)
 147                 if (sec->idx == idx)
 148                         return sec;
 149
 150         return NULL;
 151 }
 152
 153 static struct symbol *find_symbol_by_index(struct elf *elf, unsigned int idx)
 154 {
 155         struct symbol *sym;
 156
 157         elf_hash_for_each_possible(elf->symbol_hash, sym, hash, idx)
 158                 if (sym->idx == idx)
 159                         return sym;
 160
 161         return NULL;
 162 }
 163
 164 struct symbol *find_symbol_by_offset(struct section *sec, unsigned long offset)
 165 {
 166         struct rb_node *node;
 167
 168         rb_for_each(&sec->symbol_tree, node, &offset, symbol_by_offset) {
 169                 struct symbol *s = rb_entry(node, struct symbol, node);
 170
 171                 if (s->offset == offset && s->type != STT_SECTION)
 172                         return s;
 173         }
 174
 175         return NULL;
 176 }
 177
 178 struct symbol *find_func_by_offset(struct section *sec, unsigned long offset)
 179 {
 180         struct rb_node *node;
 181
 182         rb_for_each(&sec->symbol_tree, node, &offset, symbol_by_offset) {
 183                 struct symbol *s = rb_entry(node, struct symbol, node);
 184
 185                 if (s->offset == offset && s->type == STT_FUNC)
 186                         return s;
 187         }
 188
 189         return NULL;
 190 }
 191
 192 struct symbol *find_symbol_containing(const struct section *sec, unsigned long offset)
 193 {
 194         struct rb_node *node;
 195
 196         rb_for_each(&sec->symbol_tree, node, &offset, symbol_by_offset) {
 197                 struct symbol *s = rb_entry(node, struct symbol, node);
 198
 199                 if (s->type != STT_SECTION)
 200                         return s;
 201         }
 202
 203         return NULL;
 204 }
 205
 206 struct symbol *find_func_containing(struct section *sec, unsigned long offset)
 207 {
 208         struct rb_node *node;
 209
 210         rb_for_each(&sec->symbol_tree, node, &offset, symbol_by_offset) {
 211                 struct symbol *s = rb_entry(node, struct symbol, node);
 212
 213                 if (s->type == STT_FUNC)
 214                         return s;
 215         }
 216
 217         return NULL;
 218 }
 219
 220 struct symbol *find_symbol_by_name(const struct elf *elf, const char *name)
 221 {
 222         struct symbol *sym;
 223
 224         elf_hash_for_each_possible(elf->symbol_name_hash, sym, name_hash, str_hash(name))
 225                 if (!strcmp(sym->name, name))
 226                         return sym;
 227
 228         return NULL;
 229 }
 230
 231 struct reloc *find_reloc_by_dest_range(const struct elf *elf, struct section *sec,
 232                                      unsigned long offset, unsigned int len)
 233 {
 234         struct reloc *reloc, *r = NULL;
 235         unsigned long o;
 236
 237         if (!sec->reloc)
 238                 return NULL;
 239
 240         sec = sec->reloc;
 241
 242         for_offset_range(o, offset, offset + len) {
 243                 elf_hash_for_each_possible(elf->reloc_hash, reloc, hash,
 244                                        sec_offset_hash(sec, o)) {
 245                         if (reloc->sec != sec)
 246                                 continue;
 247
 248                         if (reloc->offset >= offset && reloc->offset < offset + len) {
 249                                 if (!r || reloc->offset < r->offset)
 250                                         r = reloc;
 251                         }
 252                 }
 253                 if (r)
 254                         return r;
 255         }
 256
 257         return NULL;
 258 }
 259
 260 struct reloc *find_reloc_by_dest(const struct elf *elf, struct section *sec, unsigned long offset)
 261 {
 262         return find_reloc_by_dest_range(elf, sec, offset, 1);
 263 }
 264
 265 static int read_sections(struct elf *elf)
 266 {
 267         Elf_Scn *s = NULL;
 268         struct section *sec;
 269         size_t shstrndx, sections_nr;
 270         int i;
 271
 272         if (elf_getshdrnum(elf->elf, &sections_nr)) {
 273                 WARN_ELF("elf_getshdrnum");
 274                 return -1;
 275         }
 276
 277         if (elf_getshdrstrndx(elf->elf, &shstrndx)) {
 278                 WARN_ELF("elf_getshdrstrndx");
 279                 return -1;
 280         }
 281
 282         for (i = 0; i < sections_nr; i++) {
 283                 sec = malloc(sizeof(*sec));
 284                 if (!sec) {
 285                         perror("malloc");
 286                         return -1;
 287                 }
 288                 memset(sec, 0, sizeof(*sec));
 289
 290                 INIT_LIST_HEAD(&sec->symbol_list);
 291                 INIT_LIST_HEAD(&sec->reloc_list);
 292
 293                 s = elf_getscn(elf->elf, i);
 294                 if (!s) {
 295                         WARN_ELF("elf_getscn");
 296                         return -1;
 297                 }
 298
 299                 sec->idx = elf_ndxscn(s);
 300
 301                 if (!gelf_getshdr(s, &sec->sh)) {
 302                         WARN_ELF("gelf_getshdr");
 303                         return -1;
 304                 }
 305
 306                 sec->name = elf_strptr(elf->elf, shstrndx, sec->sh.sh_name);
 307                 if (!sec->name) {
 308                         WARN_ELF("elf_strptr");
 309                         return -1;
 310                 }
 311
 312                 if (sec->sh.sh_size != 0) {
 313                         sec->data = elf_getdata(s, NULL);
 314                         if (!sec->data) {
 315                                 WARN_ELF("elf_getdata");
 316                                 return -1;
 317                         }
 318                         if (sec->data->d_off != 0 ||
 319                             sec->data->d_size != sec->sh.sh_size) {
 320                                 WARN("unexpected data attributes for %s",
 321                                      sec->name);
 322                                 return -1;
 323                         }
 324                 }
 325                 sec->len = sec->sh.sh_size;
 326
 327                 list_add_tail(&sec->list, &elf->sections);
 328                 elf_hash_add(elf->section_hash, &sec->hash, sec->idx);
 329                 elf_hash_add(elf->section_name_hash, &sec->name_hash, str_hash(sec->name));
 330         }
 331
 332         if (stats)
 333                 printf("nr_sections: %lu\n", (unsigned long)sections_nr);
 334
 335         /* sanity check, one more call to elf_nextscn() should return NULL */
 336         if (elf_nextscn(elf->elf, s)) {
 337                 WARN("section entry mismatch");
 338                 return -1;
 339         }
 340
 341         return 0;
 342 }
 343
 344 static void elf_add_symbol(struct elf *elf, struct symbol *sym)
 345 {
 346         struct list_head *entry;
 347         struct rb_node *pnode;
 348
 349         sym->alias = sym;
 350
 351         sym->type = GELF_ST_TYPE(sym->sym.st_info);
 352         sym->bind = GELF_ST_BIND(sym->sym.st_info);
 353
 354         sym->offset = sym->sym.st_value;
 355         sym->len = sym->sym.st_size;
 356
 357         rb_add(&sym->sec->symbol_tree, &sym->node, symbol_to_offset);
 358         pnode = rb_prev(&sym->node);
 359         if (pnode)
 360                 entry = &rb_entry(pnode, struct symbol, node)->list;
 361         else
 362                 entry = &sym->sec->symbol_list;
 363         list_add(&sym->list, entry);
 364         elf_hash_add(elf->symbol_hash, &sym->hash, sym->idx);
 365         elf_hash_add(elf->symbol_name_hash, &sym->name_hash, str_hash(sym->name));
 366
 367         /*
 368          * Don't store empty STT_NOTYPE symbols in the rbtree.  They
 369          * can exist within a function, confusing the sorting.
 370          */
 371         if (!sym->len)
 372                 rb_erase(&sym->node, &sym->sec->symbol_tree);
 373 }
 374
 375 static int read_symbols(struct elf *elf)
 376 {
 377         struct section *symtab, *symtab_shndx, *sec;
 378         struct symbol *sym, *pfunc;
 379         int symbols_nr, i;
 380         char *coldstr;
 381         Elf_Data *shndx_data = NULL;
 382         Elf32_Word shndx;
 383
 384         symtab = find_section_by_name(elf, ".symtab");
 385         if (!symtab) {
 386                 /*
 387                  * A missing symbol table is actually possible if it's an empty
 388                  * .o file.  This can happen for thunk_64.o.
 389                  */
 390                 return 0;
 391         }
 392
 393         symtab_shndx = find_section_by_name(elf, ".symtab_shndx");
 394         if (symtab_shndx)
 395                 shndx_data = symtab_shndx->data;
 396
 397         symbols_nr = symtab->sh.sh_size / symtab->sh.sh_entsize;
 398
 399         for (i = 0; i < symbols_nr; i++) {
 400                 sym = malloc(sizeof(*sym));
 401                 if (!sym) {
 402                         perror("malloc");
 403                         return -1;
 404                 }
 405                 memset(sym, 0, sizeof(*sym));
 406
 407                 sym->idx = i;
 408
 409                 if (!gelf_getsymshndx(symtab->data, shndx_data, i, &sym->sym,
 410                                       &shndx)) {
 411                         WARN_ELF("gelf_getsymshndx");
 412                         goto err;
 413                 }
 414
 415                 sym->name = elf_strptr(elf->elf, symtab->sh.sh_link,
 416                                        sym->sym.st_name);
 417                 if (!sym->name) {
 418                         WARN_ELF("elf_strptr");
 419                         goto err;
 420                 }
 421
 422                 if ((sym->sym.st_shndx > SHN_UNDEF &&
 423                      sym->sym.st_shndx < SHN_LORESERVE) ||
 424                     (shndx_data && sym->sym.st_shndx == SHN_XINDEX)) {
 425                         if (sym->sym.st_shndx != SHN_XINDEX)
 426                                 shndx = sym->sym.st_shndx;
 427
 428                         sym->sec = find_section_by_index(elf, shndx);
 429                         if (!sym->sec) {
 430                                 WARN("couldn't find section for symbol %s",
 431                                      sym->name);
 432                                 goto err;
 433                         }
 434                         if (GELF_ST_TYPE(sym->sym.st_info) == STT_SECTION) {
 435                                 sym->name = sym->sec->name;
 436                                 sym->sec->sym = sym;
 437                         }
 438                 } else
 439                         sym->sec = find_section_by_index(elf, 0);
 440
 441                 elf_add_symbol(elf, sym);
 442         }
 443
 444         if (stats)
 445                 printf("nr_symbols: %lu\n", (unsigned long)symbols_nr);
 446
 447         /* Create parent/child links for any cold subfunctions */
 448         list_for_each_entry(sec, &elf->sections, list) {
 449                 list_for_each_entry(sym, &sec->symbol_list, list) {
 450                         char pname[MAX_NAME_LEN + 1];
 451                         size_t pnamelen;
 452                         if (sym->type != STT_FUNC)
 453                                 continue;
 454
 455                         if (sym->pfunc == NULL)
 456                                 sym->pfunc = sym;
 457
 458                         if (sym->cfunc == NULL)
 459                                 sym->cfunc = sym;
 460
 461                         coldstr = strstr(sym->name, ".cold");
 462                         if (!coldstr)
 463                                 continue;
 464
 465                         pnamelen = coldstr - sym->name;
 466                         if (pnamelen > MAX_NAME_LEN) {
 467                                 WARN("%s(): parent function name exceeds maximum length of %d characters",
 468                                      sym->name, MAX_NAME_LEN);
 469                                 return -1;
 470                         }
 471
 472                         strncpy(pname, sym->name, pnamelen);
 473                         pname[pnamelen] = '\0';
 474                         pfunc = find_symbol_by_name(elf, pname);
 475
 476                         if (!pfunc) {
 477                                 WARN("%s(): can't find parent function",
 478                                      sym->name);
 479                                 return -1;
 480                         }
 481
 482                         sym->pfunc = pfunc;
 483                         pfunc->cfunc = sym;
 484
 485                         /*
 486                          * Unfortunately, -fnoreorder-functions puts the child
 487                          * inside the parent.  Remove the overlap so we can
 488                          * have sane assumptions.
 489                          *
 490                          * Note that pfunc->len now no longer matches
 491                          * pfunc->sym.st_size.
 492                          */
 493                         if (sym->sec == pfunc->sec &&
 494                             sym->offset >= pfunc->offset &&
 495                             sym->offset + sym->len == pfunc->offset + pfunc->len) {
 496                                 pfunc->len -= sym->len;
 497                         }
 498                 }
 499         }
 500
 501         return 0;
 502
 503 err:
 504         free(sym);
 505         return -1;
 506 }
 507
 508 static struct section *elf_create_reloc_section(struct elf *elf,
 509                                                 struct section *base,
 510                                                 int reltype);
 511
 512 int elf_add_reloc(struct elf *elf, struct section *sec, unsigned long offset,
 513                   unsigned int type, struct symbol *sym, s64 addend)
 514 {
 515         struct reloc *reloc;
 516
 517         if (!sec->reloc && !elf_create_reloc_section(elf, sec, SHT_RELA))
 518                 return -1;
 519
 520         reloc = malloc(sizeof(*reloc));
 521         if (!reloc) {
 522                 perror("malloc");
 523                 return -1;
 524         }
 525         memset(reloc, 0, sizeof(*reloc));
 526
 527         reloc->sec = sec->reloc;
 528         reloc->offset = offset;
 529         reloc->type = type;
 530         reloc->sym = sym;
 531         reloc->addend = addend;
 532
 533         list_add_tail(&reloc->list, &sec->reloc->reloc_list);
 534         elf_hash_add(elf->reloc_hash, &reloc->hash, reloc_hash(reloc));
 535
 536         sec->reloc->changed = true;
 537
 538         return 0;
 539 }
 540
 541 /*
 542  * Ensure that any reloc section containing references to @sym is marked
 543  * changed such that it will get re-generated in elf_rebuild_reloc_sections()
 544  * with the new symbol index.
 545  */
 546 static void elf_dirty_reloc_sym(struct elf *elf, struct symbol *sym)
 547 {
 548         struct section *sec;
 549
 550         list_for_each_entry(sec, &elf->sections, list) {
 551                 struct reloc *reloc;
 552
 553                 if (sec->changed)
 554                         continue;
 555
 556                 list_for_each_entry(reloc, &sec->reloc_list, list) {
 557                         if (reloc->sym == sym) {
 558                                 sec->changed = true;
 559                                 break;
 560                         }
 561                 }
 562         }
 563 }
 564
 565 /*
 566  * The libelf API is terrible; gelf_update_sym*() takes a data block relative
 567  * index value, *NOT* the symbol index. As such, iterate the data blocks and
 568  * adjust index until it fits.
 569  *
 570  * If no data block is found, allow adding a new data block provided the index
 571  * is only one past the end.
 572  */
 573 static int elf_update_symbol(struct elf *elf, struct section *symtab,
 574                              struct section *symtab_shndx, struct symbol *sym)
 575 {
 576         Elf32_Word shndx = sym->sec ? sym->sec->idx : SHN_UNDEF;
 577         Elf_Data *symtab_data = NULL, *shndx_data = NULL;
 578         Elf64_Xword entsize = symtab->sh.sh_entsize;
 579         int max_idx, idx = sym->idx;
 580         Elf_Scn *s, *t = NULL;
 581         bool is_special_shndx = sym->sym.st_shndx >= SHN_LORESERVE &&
 582                                 sym->sym.st_shndx != SHN_XINDEX;
 583
 584         if (is_special_shndx)
 585                 shndx = sym->sym.st_shndx;
 586
 587         s = elf_getscn(elf->elf, symtab->idx);
 588         if (!s) {
 589                 WARN_ELF("elf_getscn");
 590                 return -1;
 591         }
 592
 593         if (symtab_shndx) {
 594                 t = elf_getscn(elf->elf, symtab_shndx->idx);
 595                 if (!t) {
 596                         WARN_ELF("elf_getscn");
 597                         return -1;
 598                 }
 599         }
 600
 601         for (;;) {
 602                 /* get next data descriptor for the relevant sections */
 603                 symtab_data = elf_getdata(s, symtab_data);
 604                 if (t)
 605                         shndx_data = elf_getdata(t, shndx_data);
 606
 607                 /* end-of-list */
 608                 if (!symtab_data) {
 609                         void *buf;
 610
 611                         if (idx) {
 612                                 /* we don't do holes in symbol tables */
 613                                 WARN("index out of range");
 614                                 return -1;
 615                         }
 616
 617                         /* if @idx == 0, it's the next contiguous entry, create it */
 618                         symtab_data = elf_newdata(s);
 619                         if (t)
 620                                 shndx_data = elf_newdata(t);
 621
 622                         buf = calloc(1, entsize);
 623                         if (!buf) {
 624                                 WARN("malloc");
 625                                 return -1;
 626                         }
 627
 628                         symtab_data->d_buf = buf;
 629                         symtab_data->d_size = entsize;
 630                         symtab_data->d_align = 1;
 631                         symtab_data->d_type = ELF_T_SYM;
 632
 633                         symtab->sh.sh_size += entsize;
 634                         symtab->changed = true;
 635
 636                         if (t) {
 637                                 shndx_data->d_buf = &sym->sec->idx;
 638                                 shndx_data->d_size = sizeof(Elf32_Word);
 639                                 shndx_data->d_align = sizeof(Elf32_Word);
 640                                 shndx_data->d_type = ELF_T_WORD;
 641
 642                                 symtab_shndx->sh.sh_size += sizeof(Elf32_Word);
 643                                 symtab_shndx->changed = true;
 644                         }
 645
 646                         break;
 647                 }
 648
 649                 /* empty blocks should not happen */
 650                 if (!symtab_data->d_size) {
 651                         WARN("zero size data");
 652                         return -1;
 653                 }
 654
 655                 /* is this the right block? */
 656                 max_idx = symtab_data->d_size / entsize;
 657                 if (idx < max_idx)
 658                         break;
 659
 660                 /* adjust index and try again */
 661                 idx -= max_idx;
 662         }
 663
 664         /* something went side-ways */
 665         if (idx < 0) {
 666                 WARN("negative index");
 667                 return -1;
 668         }
 669
 670         /* setup extended section index magic and write the symbol */
 671         if ((shndx >= SHN_UNDEF && shndx < SHN_LORESERVE) || is_special_shndx) {
 672                 sym->sym.st_shndx = shndx;
 673                 if (!shndx_data)
 674                         shndx = 0;
 675         } else {
 676                 sym->sym.st_shndx = SHN_XINDEX;
 677                 if (!shndx_data) {
 678                         WARN("no .symtab_shndx");
 679                         return -1;
 680                 }
 681         }
 682
 683         if (!gelf_update_symshndx(symtab_data, shndx_data, idx, &sym->sym, shndx)) {
 684                 WARN_ELF("gelf_update_symshndx");
 685                 return -1;
 686         }
 687
 688         return 0;
 689 }
 690
 691 static struct symbol *
 692 elf_create_section_symbol(struct elf *elf, struct section *sec)
 693 {
 694         struct section *symtab, *symtab_shndx;
 695         Elf32_Word first_non_local, new_idx;
 696         struct symbol *sym, *old;
 697
 698         symtab = find_section_by_name(elf, ".symtab");
 699         if (symtab) {
 700                 symtab_shndx = find_section_by_name(elf, ".symtab_shndx");
 701         } else {
 702                 WARN("no .symtab");
 703                 return NULL;
 704         }
 705
 706         sym = calloc(1, sizeof(*sym));
 707         if (!sym) {
 708                 perror("malloc");
 709                 return NULL;
 710         }
 711
 712         sym->name = sec->name;
 713         sym->sec = sec;
 714
 715         // st_name 0
 716         sym->sym.st_info = GELF_ST_INFO(STB_LOCAL, STT_SECTION);
 717         // st_other 0
 718         // st_value 0
 719         // st_size 0
 720
 721         /*
 722          * Move the first global symbol, as per sh_info, into a new, higher
 723          * symbol index. This fees up a spot for a new local symbol.
 724          */
 725         first_non_local = symtab->sh.sh_info;
 726         new_idx = symtab->sh.sh_size / symtab->sh.sh_entsize;
 727         old = find_symbol_by_index(elf, first_non_local);
 728         if (old) {
 729                 old->idx = new_idx;
 730
 731                 hlist_del(&old->hash);
 732                 elf_hash_add(elf->symbol_hash, &old->hash, old->idx);
 733
 734                 elf_dirty_reloc_sym(elf, old);
 735
 736                 if (elf_update_symbol(elf, symtab, symtab_shndx, old)) {
 737                         WARN("elf_update_symbol move");
 738                         return NULL;
 739                 }
 740
 741                 new_idx = first_non_local;
 742         }
 743
 744         sym->idx = new_idx;
 745         if (elf_update_symbol(elf, symtab, symtab_shndx, sym)) {
 746                 WARN("elf_update_symbol");
 747                 return NULL;
 748         }
 749
 750         /*
 751          * Either way, we added a LOCAL symbol.
 752          */
 753         symtab->sh.sh_info += 1;
 754
 755         elf_add_symbol(elf, sym);
 756
 757         return sym;
 758 }
 759
 760 int elf_add_reloc_to_insn(struct elf *elf, struct section *sec,
 761                           unsigned long offset, unsigned int type,
 762                           struct section *insn_sec, unsigned long insn_off)
 763 {
 764         struct symbol *sym = insn_sec->sym;
 765         int addend = insn_off;
 766
 767         if (!sym) {
 768                 /*
 769                  * Due to how weak functions work, we must use section based
 770                  * relocations. Symbol based relocations would result in the
 771                  * weak and non-weak function annotations being overlaid on the
 772                  * non-weak function after linking.
 773                  */
 774                 sym = elf_create_section_symbol(elf, insn_sec);
 775                 if (!sym)
 776                         return -1;
 777
 778                 insn_sec->sym = sym;
 779         }
 780
 781         return elf_add_reloc(elf, sec, offset, type, sym, addend);
 782 }
 783
 784 static int read_rel_reloc(struct section *sec, int i, struct reloc *reloc, unsigned int *symndx)
 785 {
 786         if (!gelf_getrel(sec->data, i, &reloc->rel)) {
 787                 WARN_ELF("gelf_getrel");
 788                 return -1;
 789         }
 790         reloc->type = GELF_R_TYPE(reloc->rel.r_info);
 791         reloc->addend = 0;
 792         reloc->offset = reloc->rel.r_offset;
 793         *symndx = GELF_R_SYM(reloc->rel.r_info);
 794         return 0;
 795 }
 796
 797 static int read_rela_reloc(struct section *sec, int i, struct reloc *reloc, unsigned int *symndx)
 798 {
 799         if (!gelf_getrela(sec->data, i, &reloc->rela)) {
 800                 WARN_ELF("gelf_getrela");
 801                 return -1;
 802         }
 803         reloc->type = GELF_R_TYPE(reloc->rela.r_info);
 804         reloc->addend = reloc->rela.r_addend;
 805         reloc->offset = reloc->rela.r_offset;
 806         *symndx = GELF_R_SYM(reloc->rela.r_info);
 807         return 0;
 808 }
 809
 810 static int read_relocs(struct elf *elf)
 811 {
 812         struct section *sec;
 813         struct reloc *reloc;
 814         int i;
 815         unsigned int symndx;
 816         unsigned long nr_reloc, max_reloc = 0, tot_reloc = 0;
 817
 818         list_for_each_entry(sec, &elf->sections, list) {
 819                 if ((sec->sh.sh_type != SHT_RELA) &&
 820                     (sec->sh.sh_type != SHT_REL))
 821                         continue;
 822
 823                 sec->base = find_section_by_index(elf, sec->sh.sh_info);
 824                 if (!sec->base) {
 825                         WARN("can't find base section for reloc section %s",
 826                              sec->name);
 827                         return -1;
 828                 }
 829
 830                 sec->base->reloc = sec;
 831
 832                 nr_reloc = 0;
 833                 for (i = 0; i < sec->sh.sh_size / sec->sh.sh_entsize; i++) {
 834                         reloc = malloc(sizeof(*reloc));
 835                         if (!reloc) {
 836                                 perror("malloc");
 837                                 return -1;
 838                         }
 839                         memset(reloc, 0, sizeof(*reloc));
 840                         switch (sec->sh.sh_type) {
 841                         case SHT_REL:
 842                                 if (read_rel_reloc(sec, i, reloc, &symndx))
 843                                         return -1;
 844                                 break;
 845                         case SHT_RELA:
 846                                 if (read_rela_reloc(sec, i, reloc, &symndx))
 847                                         return -1;
 848                                 break;
 849                         default: return -1;
 850                         }
 851
 852                         reloc->sec = sec;
 853                         reloc->idx = i;
 854                         reloc->sym = find_symbol_by_index(elf, symndx);
 855                         if (!reloc->sym) {
 856                                 WARN("can't find reloc entry symbol %d for %s",
 857                                      symndx, sec->name);
 858                                 return -1;
 859                         }
 860
 861                         list_add_tail(&reloc->list, &sec->reloc_list);
 862                         elf_hash_add(elf->reloc_hash, &reloc->hash, reloc_hash(reloc));
 863
 864                         nr_reloc++;
 865                 }
 866                 max_reloc = max(max_reloc, nr_reloc);
 867                 tot_reloc += nr_reloc;
 868         }
 869
 870         if (stats) {
 871                 printf("max_reloc: %lu\n", max_reloc);
 872                 printf("tot_reloc: %lu\n", tot_reloc);
 873         }
 874
 875         return 0;
 876 }
 877
 878 struct elf *elf_open_read(const char *name, int flags)
 879 {
 880         struct elf *elf;
 881         Elf_Cmd cmd;
 882
 883         elf_version(EV_CURRENT);
 884
 885         elf = malloc(sizeof(*elf));
 886         if (!elf) {
 887                 perror("malloc");
 888                 return NULL;
 889         }
 890         memset(elf, 0, offsetof(struct elf, sections));
 891
 892         INIT_LIST_HEAD(&elf->sections);
 893
 894         elf_hash_init(elf->symbol_hash);
 895         elf_hash_init(elf->symbol_name_hash);
 896         elf_hash_init(elf->section_hash);
 897         elf_hash_init(elf->section_name_hash);
 898         elf_hash_init(elf->reloc_hash);
 899
 900         elf->fd = open(name, flags);
 901         if (elf->fd == -1) {
 902                 fprintf(stderr, "objtool: Can't open '%s': %s\n",
 903                         name, strerror(errno));
 904                 goto err;
 905         }
 906
 907         if ((flags & O_ACCMODE) == O_RDONLY)
 908                 cmd = ELF_C_READ_MMAP;
 909         else if ((flags & O_ACCMODE) == O_RDWR)
 910                 cmd = ELF_C_RDWR;
 911         else /* O_WRONLY */
 912                 cmd = ELF_C_WRITE;
 913
 914         elf->elf = elf_begin(elf->fd, cmd, NULL);
 915         if (!elf->elf) {
 916                 WARN_ELF("elf_begin");
 917                 goto err;
 918         }
 919
 920         if (!gelf_getehdr(elf->elf, &elf->ehdr)) {
 921                 WARN_ELF("gelf_getehdr");
 922                 goto err;
 923         }
 924
 925         if (read_sections(elf))
 926                 goto err;
 927
 928         if (read_symbols(elf))
 929                 goto err;
 930
 931         if (read_relocs(elf))
 932                 goto err;
 933
 934         return elf;
 935
 936 err:
 937         elf_close(elf);
 938         return NULL;
 939 }
 940
 941 static int elf_add_string(struct elf *elf, struct section *strtab, char *str)
 942 {
 943         Elf_Data *data;
 944         Elf_Scn *s;
 945         int len;
 946
 947         if (!strtab)
 948                 strtab = find_section_by_name(elf, ".strtab");
 949         if (!strtab) {
 950                 WARN("can't find .strtab section");
 951                 return -1;
 952         }
 953
 954         s = elf_getscn(elf->elf, strtab->idx);
 955         if (!s) {
 956                 WARN_ELF("elf_getscn");
 957                 return -1;
 958         }
 959
 960         data = elf_newdata(s);
 961         if (!data) {
 962                 WARN_ELF("elf_newdata");
 963                 return -1;
 964         }
 965
 966         data->d_buf = str;
 967         data->d_size = strlen(str) + 1;
 968         data->d_align = 1;
 969         data->d_type = ELF_T_SYM;
 970
 971         len = strtab->len;
 972         strtab->len += data->d_size;
 973         strtab->changed = true;
 974
 975         return len;
 976 }
 977
 978 struct section *elf_create_section(struct elf *elf, const char *name,
 979                                    unsigned int sh_flags, size_t entsize, int nr)
 980 {
 981         struct section *sec, *shstrtab;
 982         size_t size = entsize * nr;
 983         Elf_Scn *s;
 984
 985         sec = malloc(sizeof(*sec));
 986         if (!sec) {
 987                 perror("malloc");
 988                 return NULL;
 989         }
 990         memset(sec, 0, sizeof(*sec));
 991
 992         INIT_LIST_HEAD(&sec->symbol_list);
 993         INIT_LIST_HEAD(&sec->reloc_list);
 994
 995         s = elf_newscn(elf->elf);
 996         if (!s) {
 997                 WARN_ELF("elf_newscn");
 998                 return NULL;
 999         }
1000
1001         sec->name = strdup(name);
1002         if (!sec->name) {
1003                 perror("strdup");
1004                 return NULL;
1005         }
1006
1007         sec->idx = elf_ndxscn(s);
1008         sec->len = size;
1009         sec->changed = true;
1010
1011         sec->data = elf_newdata(s);
1012         if (!sec->data) {
1013                 WARN_ELF("elf_newdata");
1014                 return NULL;
1015         }
1016
1017         sec->data->d_size = size;
1018         sec->data->d_align = 1;
1019
1020         if (size) {
1021                 sec->data->d_buf = malloc(size);
1022                 if (!sec->data->d_buf) {
1023                         perror("malloc");
1024                         return NULL;
1025                 }
1026                 memset(sec->data->d_buf, 0, size);
1027         }
1028
1029         if (!gelf_getshdr(s, &sec->sh)) {
1030                 WARN_ELF("gelf_getshdr");
1031                 return NULL;
1032         }
1033
1034         sec->sh.sh_size = size;
1035         sec->sh.sh_entsize = entsize;
1036         sec->sh.sh_type = SHT_PROGBITS;
1037         sec->sh.sh_addralign = 1;
1038         sec->sh.sh_flags = SHF_ALLOC | sh_flags;
1039
1040         /* Add section name to .shstrtab (or .strtab for Clang) */
1041         shstrtab = find_section_by_name(elf, ".shstrtab");
1042         if (!shstrtab)
1043                 shstrtab = find_section_by_name(elf, ".strtab");
1044         if (!shstrtab) {
1045                 WARN("can't find .shstrtab or .strtab section");
1046                 return NULL;
1047         }
1048         sec->sh.sh_name = elf_add_string(elf, shstrtab, sec->name);
1049         if (sec->sh.sh_name == -1)
1050                 return NULL;
1051
1052         list_add_tail(&sec->list, &elf->sections);
1053         elf_hash_add(elf->section_hash, &sec->hash, sec->idx);
1054         elf_hash_add(elf->section_name_hash, &sec->name_hash, str_hash(sec->name));
1055
1056         elf->changed = true;
1057
1058         return sec;
1059 }
1060
1061 static struct section *elf_create_rel_reloc_section(struct elf *elf, struct section *base)
1062 {
1063         char *relocname;
1064         struct section *sec;
1065
1066         relocname = malloc(strlen(base->name) + strlen(".rel") + 1);
1067         if (!relocname) {
1068                 perror("malloc");
1069                 return NULL;
1070         }
1071         strcpy(relocname, ".rel");
1072         strcat(relocname, base->name);
1073
1074         sec = elf_create_section(elf, relocname, 0, sizeof(GElf_Rel), 0);
1075         free(relocname);
1076         if (!sec)
1077                 return NULL;
1078
1079         base->reloc = sec;
1080         sec->base = base;
1081
1082         sec->sh.sh_type = SHT_REL;
1083         sec->sh.sh_addralign = 8;
1084         sec->sh.sh_link = find_section_by_name(elf, ".symtab")->idx;
1085         sec->sh.sh_info = base->idx;
1086         sec->sh.sh_flags = SHF_INFO_LINK;
1087
1088         return sec;
1089 }
1090
1091 static struct section *elf_create_rela_reloc_section(struct elf *elf, struct section *base)
1092 {
1093         char *relocname;
1094         struct section *sec;
1095
1096         relocname = malloc(strlen(base->name) + strlen(".rela") + 1);
1097         if (!relocname) {
1098                 perror("malloc");
1099                 return NULL;
1100         }
1101         strcpy(relocname, ".rela");
1102         strcat(relocname, base->name);
1103
1104         sec = elf_create_section(elf, relocname, 0, sizeof(GElf_Rela), 0);
1105         free(relocname);
1106         if (!sec)
1107                 return NULL;
1108
1109         base->reloc = sec;
1110         sec->base = base;
1111
1112         sec->sh.sh_type = SHT_RELA;
1113         sec->sh.sh_addralign = 8;
1114         sec->sh.sh_link = find_section_by_name(elf, ".symtab")->idx;
1115         sec->sh.sh_info = base->idx;
1116         sec->sh.sh_flags = SHF_INFO_LINK;
1117
1118         return sec;
1119 }
1120
1121 static struct section *elf_create_reloc_section(struct elf *elf,
1122                                          struct section *base,
1123                                          int reltype)
1124 {
1125         switch (reltype) {
1126         case SHT_REL:  return elf_create_rel_reloc_section(elf, base);
1127         case SHT_RELA: return elf_create_rela_reloc_section(elf, base);
1128         default:       return NULL;
1129         }
1130 }
1131
1132 static int elf_rebuild_rel_reloc_section(struct section *sec, int nr)
1133 {
1134         struct reloc *reloc;
1135         int idx = 0, size;
1136         GElf_Rel *relocs;
1137
1138         /* Allocate a buffer for relocations */
1139         size = nr * sizeof(*relocs);
1140         relocs = malloc(size);
1141         if (!relocs) {
1142                 perror("malloc");
1143                 return -1;
1144         }
1145
1146         sec->data->d_buf = relocs;
1147         sec->data->d_size = size;
1148
1149         sec->sh.sh_size = size;
1150
1151         idx = 0;
1152         list_for_each_entry(reloc, &sec->reloc_list, list) {
1153                 relocs[idx].r_offset = reloc->offset;
1154                 relocs[idx].r_info = GELF_R_INFO(reloc->sym->idx, reloc->type);
1155                 idx++;
1156         }
1157
1158         return 0;
1159 }
1160
1161 static int elf_rebuild_rela_reloc_section(struct section *sec, int nr)
1162 {
1163         struct reloc *reloc;
1164         int idx = 0, size;
1165         GElf_Rela *relocs;
1166
1167         /* Allocate a buffer for relocations with addends */
1168         size = nr * sizeof(*relocs);
1169         relocs = malloc(size);
1170         if (!relocs) {
1171                 perror("malloc");
1172                 return -1;
1173         }
1174
1175         sec->data->d_buf = relocs;
1176         sec->data->d_size = size;
1177
1178         sec->sh.sh_size = size;
1179
1180         idx = 0;
1181         list_for_each_entry(reloc, &sec->reloc_list, list) {
1182                 relocs[idx].r_offset = reloc->offset;
1183                 relocs[idx].r_addend = reloc->addend;
1184                 relocs[idx].r_info = GELF_R_INFO(reloc->sym->idx, reloc->type);
1185                 idx++;
1186         }
1187
1188         return 0;
1189 }
1190
1191 static int elf_rebuild_reloc_section(struct elf *elf, struct section *sec)
1192 {
1193         struct reloc *reloc;
1194         int nr;
1195
1196         nr = 0;
1197         list_for_each_entry(reloc, &sec->reloc_list, list)
1198                 nr++;
1199
1200         switch (sec->sh.sh_type) {
1201         case SHT_REL:  return elf_rebuild_rel_reloc_section(sec, nr);
1202         case SHT_RELA: return elf_rebuild_rela_reloc_section(sec, nr);
1203         default:       return -1;
1204         }
1205 }
1206
1207 int elf_write_insn(struct elf *elf, struct section *sec,
1208                    unsigned long offset, unsigned int len,
1209                    const char *insn)
1210 {
1211         Elf_Data *data = sec->data;
1212
1213         if (data->d_type != ELF_T_BYTE || data->d_off) {
1214                 WARN("write to unexpected data for section: %s", sec->name);
1215                 return -1;
1216         }
1217
1218         memcpy(data->d_buf + offset, insn, len);
1219         elf_flagdata(data, ELF_C_SET, ELF_F_DIRTY);
1220
1221         elf->changed = true;
1222
1223         return 0;
1224 }
1225
1226 int elf_write_reloc(struct elf *elf, struct reloc *reloc)
1227 {
1228         struct section *sec = reloc->sec;
1229
1230         if (sec->sh.sh_type == SHT_REL) {
1231                 reloc->rel.r_info = GELF_R_INFO(reloc->sym->idx, reloc->type);
1232                 reloc->rel.r_offset = reloc->offset;
1233
1234                 if (!gelf_update_rel(sec->data, reloc->idx, &reloc->rel)) {
1235                         WARN_ELF("gelf_update_rel");
1236                         return -1;
1237                 }
1238         } else {
1239                 reloc->rela.r_info = GELF_R_INFO(reloc->sym->idx, reloc->type);
1240                 reloc->rela.r_addend = reloc->addend;
1241                 reloc->rela.r_offset = reloc->offset;
1242
1243                 if (!gelf_update_rela(sec->data, reloc->idx, &reloc->rela)) {
1244                         WARN_ELF("gelf_update_rela");
1245                         return -1;
1246                 }
1247         }
1248
1249         elf->changed = true;
1250
1251         return 0;
1252 }
1253
1254 int elf_write(struct elf *elf)
1255 {
1256         struct section *sec;
1257         Elf_Scn *s;
1258
1259         /* Update changed relocation sections and section headers: */
1260         list_for_each_entry(sec, &elf->sections, list) {
1261                 if (sec->changed) {
1262                         if (sec->base &&
1263                             elf_rebuild_reloc_section(elf, sec)) {
1264                                 WARN("elf_rebuild_reloc_section");
1265                                 return -1;
1266                         }
1267
1268                         s = elf_getscn(elf->elf, sec->idx);
1269                         if (!s) {
1270                                 WARN_ELF("elf_getscn");
1271                                 return -1;
1272                         }
1273                         if (!gelf_update_shdr(s, &sec->sh)) {
1274                                 WARN_ELF("gelf_update_shdr");
1275                                 return -1;
1276                         }
1277
1278                         sec->changed = false;
1279                         elf->changed = true;
1280                 }
1281         }
1282
1283         /* Make sure the new section header entries get updated properly. */
1284         elf_flagelf(elf->elf, ELF_C_SET, ELF_F_DIRTY);
1285
1286         /* Write all changes to the file. */
1287         if (elf_update(elf->elf, ELF_C_WRITE) < 0) {
1288                 WARN_ELF("elf_update");
1289                 return -1;
1290         }
1291
1292         elf->changed = false;
1293
1294         return 0;
1295 }
1296
1297 void elf_close(struct elf *elf)
1298 {
1299         struct section *sec, *tmpsec;
1300         struct symbol *sym, *tmpsym;
1301         struct reloc *reloc, *tmpreloc;
1302
1303         if (elf->elf)
1304                 elf_end(elf->elf);
1305
1306         if (elf->fd > 0)
1307                 close(elf->fd);
1308
1309         list_for_each_entry_safe(sec, tmpsec, &elf->sections, list) {
1310                 list_for_each_entry_safe(sym, tmpsym, &sec->symbol_list, list) {
1311                         list_del(&sym->list);
1312                         hash_del(&sym->hash);
1313                         free(sym);
1314                 }
1315                 list_for_each_entry_safe(reloc, tmpreloc, &sec->reloc_list, list) {
1316                         list_del(&reloc->list);
1317                         hash_del(&reloc->hash);
1318                         free(reloc);
1319                 }
1320                 list_del(&sec->list);
1321                 free(sec);
1322         }
1323
1324         free(elf);
1325 }