1352 lines · c
1// SPDX-License-Identifier: GPL-2.0-or-later2/*3 * elf.c - ELF access library4 *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 <linux/interval_tree_generic.h>20#include <objtool/builtin.h>21 22#include <objtool/elf.h>23#include <objtool/warn.h>24 25static inline u32 str_hash(const char *str)26{27 return jhash(str, strlen(str), 0);28}29 30#define __elf_table(name) (elf->name##_hash)31#define __elf_bits(name) (elf->name##_bits)32 33#define __elf_table_entry(name, key) \34 __elf_table(name)[hash_min(key, __elf_bits(name))]35 36#define elf_hash_add(name, node, key) \37({ \38 struct elf_hash_node *__node = node; \39 __node->next = __elf_table_entry(name, key); \40 __elf_table_entry(name, key) = __node; \41})42 43static inline void __elf_hash_del(struct elf_hash_node *node,44 struct elf_hash_node **head)45{46 struct elf_hash_node *cur, *prev;47 48 if (node == *head) {49 *head = node->next;50 return;51 }52 53 for (prev = NULL, cur = *head; cur; prev = cur, cur = cur->next) {54 if (cur == node) {55 prev->next = cur->next;56 break;57 }58 }59}60 61#define elf_hash_del(name, node, key) \62 __elf_hash_del(node, &__elf_table_entry(name, key))63 64#define elf_list_entry(ptr, type, member) \65({ \66 typeof(ptr) __ptr = (ptr); \67 __ptr ? container_of(__ptr, type, member) : NULL; \68})69 70#define elf_hash_for_each_possible(name, obj, member, key) \71 for (obj = elf_list_entry(__elf_table_entry(name, key), typeof(*obj), member); \72 obj; \73 obj = elf_list_entry(obj->member.next, typeof(*(obj)), member))74 75#define elf_alloc_hash(name, size) \76({ \77 __elf_bits(name) = max(10, ilog2(size)); \78 __elf_table(name) = mmap(NULL, sizeof(struct elf_hash_node *) << __elf_bits(name), \79 PROT_READ|PROT_WRITE, \80 MAP_PRIVATE|MAP_ANON, -1, 0); \81 if (__elf_table(name) == (void *)-1L) { \82 WARN("mmap fail " #name); \83 __elf_table(name) = NULL; \84 } \85 __elf_table(name); \86})87 88static inline unsigned long __sym_start(struct symbol *s)89{90 return s->offset;91}92 93static inline unsigned long __sym_last(struct symbol *s)94{95 return s->offset + s->len - 1;96}97 98INTERVAL_TREE_DEFINE(struct symbol, node, unsigned long, __subtree_last,99 __sym_start, __sym_last, static, __sym)100 101#define __sym_for_each(_iter, _tree, _start, _end) \102 for (_iter = __sym_iter_first((_tree), (_start), (_end)); \103 _iter; _iter = __sym_iter_next(_iter, (_start), (_end)))104 105struct symbol_hole {106 unsigned long key;107 const struct symbol *sym;108};109 110/*111 * Find !section symbol where @offset is after it.112 */113static int symbol_hole_by_offset(const void *key, const struct rb_node *node)114{115 const struct symbol *s = rb_entry(node, struct symbol, node);116 struct symbol_hole *sh = (void *)key;117 118 if (sh->key < s->offset)119 return -1;120 121 if (sh->key >= s->offset + s->len) {122 if (s->type != STT_SECTION)123 sh->sym = s;124 return 1;125 }126 127 return 0;128}129 130struct section *find_section_by_name(const struct elf *elf, const char *name)131{132 struct section *sec;133 134 elf_hash_for_each_possible(section_name, sec, name_hash, str_hash(name)) {135 if (!strcmp(sec->name, name))136 return sec;137 }138 139 return NULL;140}141 142static struct section *find_section_by_index(struct elf *elf,143 unsigned int idx)144{145 struct section *sec;146 147 elf_hash_for_each_possible(section, sec, hash, idx) {148 if (sec->idx == idx)149 return sec;150 }151 152 return NULL;153}154 155static struct symbol *find_symbol_by_index(struct elf *elf, unsigned int idx)156{157 struct symbol *sym;158 159 elf_hash_for_each_possible(symbol, sym, hash, idx) {160 if (sym->idx == idx)161 return sym;162 }163 164 return NULL;165}166 167struct symbol *find_symbol_by_offset(struct section *sec, unsigned long offset)168{169 struct rb_root_cached *tree = (struct rb_root_cached *)&sec->symbol_tree;170 struct symbol *iter;171 172 __sym_for_each(iter, tree, offset, offset) {173 if (iter->offset == offset && iter->type != STT_SECTION)174 return iter;175 }176 177 return NULL;178}179 180struct symbol *find_func_by_offset(struct section *sec, unsigned long offset)181{182 struct rb_root_cached *tree = (struct rb_root_cached *)&sec->symbol_tree;183 struct symbol *iter;184 185 __sym_for_each(iter, tree, offset, offset) {186 if (iter->offset == offset && iter->type == STT_FUNC)187 return iter;188 }189 190 return NULL;191}192 193struct symbol *find_symbol_containing(const struct section *sec, unsigned long offset)194{195 struct rb_root_cached *tree = (struct rb_root_cached *)&sec->symbol_tree;196 struct symbol *iter;197 198 __sym_for_each(iter, tree, offset, offset) {199 if (iter->type != STT_SECTION)200 return iter;201 }202 203 return NULL;204}205 206/*207 * Returns size of hole starting at @offset.208 */209int find_symbol_hole_containing(const struct section *sec, unsigned long offset)210{211 struct symbol_hole hole = {212 .key = offset,213 .sym = NULL,214 };215 struct rb_node *n;216 struct symbol *s;217 218 /*219 * Find the rightmost symbol for which @offset is after it.220 */221 n = rb_find(&hole, &sec->symbol_tree.rb_root, symbol_hole_by_offset);222 223 /* found a symbol that contains @offset */224 if (n)225 return 0; /* not a hole */226 227 /* didn't find a symbol for which @offset is after it */228 if (!hole.sym)229 return 0; /* not a hole */230 231 /* @offset >= sym->offset + sym->len, find symbol after it */232 n = rb_next(&hole.sym->node);233 if (!n)234 return -1; /* until end of address space */235 236 /* hole until start of next symbol */237 s = rb_entry(n, struct symbol, node);238 return s->offset - offset;239}240 241struct symbol *find_func_containing(struct section *sec, unsigned long offset)242{243 struct rb_root_cached *tree = (struct rb_root_cached *)&sec->symbol_tree;244 struct symbol *iter;245 246 __sym_for_each(iter, tree, offset, offset) {247 if (iter->type == STT_FUNC)248 return iter;249 }250 251 return NULL;252}253 254struct symbol *find_symbol_by_name(const struct elf *elf, const char *name)255{256 struct symbol *sym;257 258 elf_hash_for_each_possible(symbol_name, sym, name_hash, str_hash(name)) {259 if (!strcmp(sym->name, name))260 return sym;261 }262 263 return NULL;264}265 266struct reloc *find_reloc_by_dest_range(const struct elf *elf, struct section *sec,267 unsigned long offset, unsigned int len)268{269 struct reloc *reloc, *r = NULL;270 struct section *rsec;271 unsigned long o;272 273 rsec = sec->rsec;274 if (!rsec)275 return NULL;276 277 for_offset_range(o, offset, offset + len) {278 elf_hash_for_each_possible(reloc, reloc, hash,279 sec_offset_hash(rsec, o)) {280 if (reloc->sec != rsec)281 continue;282 283 if (reloc_offset(reloc) >= offset &&284 reloc_offset(reloc) < offset + len) {285 if (!r || reloc_offset(reloc) < reloc_offset(r))286 r = reloc;287 }288 }289 if (r)290 return r;291 }292 293 return NULL;294}295 296struct reloc *find_reloc_by_dest(const struct elf *elf, struct section *sec, unsigned long offset)297{298 return find_reloc_by_dest_range(elf, sec, offset, 1);299}300 301static bool is_dwarf_section(struct section *sec)302{303 return !strncmp(sec->name, ".debug_", 7);304}305 306static int read_sections(struct elf *elf)307{308 Elf_Scn *s = NULL;309 struct section *sec;310 size_t shstrndx, sections_nr;311 int i;312 313 if (elf_getshdrnum(elf->elf, §ions_nr)) {314 WARN_ELF("elf_getshdrnum");315 return -1;316 }317 318 if (elf_getshdrstrndx(elf->elf, &shstrndx)) {319 WARN_ELF("elf_getshdrstrndx");320 return -1;321 }322 323 if (!elf_alloc_hash(section, sections_nr) ||324 !elf_alloc_hash(section_name, sections_nr))325 return -1;326 327 elf->section_data = calloc(sections_nr, sizeof(*sec));328 if (!elf->section_data) {329 perror("calloc");330 return -1;331 }332 for (i = 0; i < sections_nr; i++) {333 sec = &elf->section_data[i];334 335 INIT_LIST_HEAD(&sec->symbol_list);336 337 s = elf_getscn(elf->elf, i);338 if (!s) {339 WARN_ELF("elf_getscn");340 return -1;341 }342 343 sec->idx = elf_ndxscn(s);344 345 if (!gelf_getshdr(s, &sec->sh)) {346 WARN_ELF("gelf_getshdr");347 return -1;348 }349 350 sec->name = elf_strptr(elf->elf, shstrndx, sec->sh.sh_name);351 if (!sec->name) {352 WARN_ELF("elf_strptr");353 return -1;354 }355 356 if (sec->sh.sh_size != 0 && !is_dwarf_section(sec)) {357 sec->data = elf_getdata(s, NULL);358 if (!sec->data) {359 WARN_ELF("elf_getdata");360 return -1;361 }362 if (sec->data->d_off != 0 ||363 sec->data->d_size != sec->sh.sh_size) {364 WARN("unexpected data attributes for %s",365 sec->name);366 return -1;367 }368 }369 370 list_add_tail(&sec->list, &elf->sections);371 elf_hash_add(section, &sec->hash, sec->idx);372 elf_hash_add(section_name, &sec->name_hash, str_hash(sec->name));373 374 if (is_reloc_sec(sec))375 elf->num_relocs += sec_num_entries(sec);376 }377 378 if (opts.stats) {379 printf("nr_sections: %lu\n", (unsigned long)sections_nr);380 printf("section_bits: %d\n", elf->section_bits);381 }382 383 /* sanity check, one more call to elf_nextscn() should return NULL */384 if (elf_nextscn(elf->elf, s)) {385 WARN("section entry mismatch");386 return -1;387 }388 389 return 0;390}391 392static void elf_add_symbol(struct elf *elf, struct symbol *sym)393{394 struct list_head *entry;395 struct rb_node *pnode;396 struct symbol *iter;397 398 INIT_LIST_HEAD(&sym->pv_target);399 sym->alias = sym;400 401 sym->type = GELF_ST_TYPE(sym->sym.st_info);402 sym->bind = GELF_ST_BIND(sym->sym.st_info);403 404 if (sym->type == STT_FILE)405 elf->num_files++;406 407 sym->offset = sym->sym.st_value;408 sym->len = sym->sym.st_size;409 410 __sym_for_each(iter, &sym->sec->symbol_tree, sym->offset, sym->offset) {411 if (iter->offset == sym->offset && iter->type == sym->type)412 iter->alias = sym;413 }414 415 __sym_insert(sym, &sym->sec->symbol_tree);416 pnode = rb_prev(&sym->node);417 if (pnode)418 entry = &rb_entry(pnode, struct symbol, node)->list;419 else420 entry = &sym->sec->symbol_list;421 list_add(&sym->list, entry);422 elf_hash_add(symbol, &sym->hash, sym->idx);423 elf_hash_add(symbol_name, &sym->name_hash, str_hash(sym->name));424 425 /*426 * Don't store empty STT_NOTYPE symbols in the rbtree. They427 * can exist within a function, confusing the sorting.428 */429 if (!sym->len)430 __sym_remove(sym, &sym->sec->symbol_tree);431}432 433static int read_symbols(struct elf *elf)434{435 struct section *symtab, *symtab_shndx, *sec;436 struct symbol *sym, *pfunc;437 int symbols_nr, i;438 char *coldstr;439 Elf_Data *shndx_data = NULL;440 Elf32_Word shndx;441 442 symtab = find_section_by_name(elf, ".symtab");443 if (symtab) {444 symtab_shndx = find_section_by_name(elf, ".symtab_shndx");445 if (symtab_shndx)446 shndx_data = symtab_shndx->data;447 448 symbols_nr = sec_num_entries(symtab);449 } else {450 /*451 * A missing symbol table is actually possible if it's an empty452 * .o file. This can happen for thunk_64.o. Make sure to at453 * least allocate the symbol hash tables so we can do symbol454 * lookups without crashing.455 */456 symbols_nr = 0;457 }458 459 if (!elf_alloc_hash(symbol, symbols_nr) ||460 !elf_alloc_hash(symbol_name, symbols_nr))461 return -1;462 463 elf->symbol_data = calloc(symbols_nr, sizeof(*sym));464 if (!elf->symbol_data) {465 perror("calloc");466 return -1;467 }468 for (i = 0; i < symbols_nr; i++) {469 sym = &elf->symbol_data[i];470 471 sym->idx = i;472 473 if (!gelf_getsymshndx(symtab->data, shndx_data, i, &sym->sym,474 &shndx)) {475 WARN_ELF("gelf_getsymshndx");476 goto err;477 }478 479 sym->name = elf_strptr(elf->elf, symtab->sh.sh_link,480 sym->sym.st_name);481 if (!sym->name) {482 WARN_ELF("elf_strptr");483 goto err;484 }485 486 if ((sym->sym.st_shndx > SHN_UNDEF &&487 sym->sym.st_shndx < SHN_LORESERVE) ||488 (shndx_data && sym->sym.st_shndx == SHN_XINDEX)) {489 if (sym->sym.st_shndx != SHN_XINDEX)490 shndx = sym->sym.st_shndx;491 492 sym->sec = find_section_by_index(elf, shndx);493 if (!sym->sec) {494 WARN("couldn't find section for symbol %s",495 sym->name);496 goto err;497 }498 if (GELF_ST_TYPE(sym->sym.st_info) == STT_SECTION) {499 sym->name = sym->sec->name;500 sym->sec->sym = sym;501 }502 } else503 sym->sec = find_section_by_index(elf, 0);504 505 elf_add_symbol(elf, sym);506 }507 508 if (opts.stats) {509 printf("nr_symbols: %lu\n", (unsigned long)symbols_nr);510 printf("symbol_bits: %d\n", elf->symbol_bits);511 }512 513 /* Create parent/child links for any cold subfunctions */514 list_for_each_entry(sec, &elf->sections, list) {515 sec_for_each_sym(sec, sym) {516 char *pname;517 size_t pnamelen;518 if (sym->type != STT_FUNC)519 continue;520 521 if (sym->pfunc == NULL)522 sym->pfunc = sym;523 524 if (sym->cfunc == NULL)525 sym->cfunc = sym;526 527 coldstr = strstr(sym->name, ".cold");528 if (!coldstr)529 continue;530 531 pnamelen = coldstr - sym->name;532 pname = strndup(sym->name, pnamelen);533 if (!pname) {534 WARN("%s(): failed to allocate memory",535 sym->name);536 return -1;537 }538 539 pfunc = find_symbol_by_name(elf, pname);540 free(pname);541 542 if (!pfunc) {543 WARN("%s(): can't find parent function",544 sym->name);545 return -1;546 }547 548 sym->pfunc = pfunc;549 pfunc->cfunc = sym;550 551 /*552 * Unfortunately, -fnoreorder-functions puts the child553 * inside the parent. Remove the overlap so we can554 * have sane assumptions.555 *556 * Note that pfunc->len now no longer matches557 * pfunc->sym.st_size.558 */559 if (sym->sec == pfunc->sec &&560 sym->offset >= pfunc->offset &&561 sym->offset + sym->len == pfunc->offset + pfunc->len) {562 pfunc->len -= sym->len;563 }564 }565 }566 567 return 0;568 569err:570 free(sym);571 return -1;572}573 574/*575 * @sym's idx has changed. Update the relocs which reference it.576 */577static int elf_update_sym_relocs(struct elf *elf, struct symbol *sym)578{579 struct reloc *reloc;580 581 for (reloc = sym->relocs; reloc; reloc = reloc->sym_next_reloc)582 set_reloc_sym(elf, reloc, reloc->sym->idx);583 584 return 0;585}586 587/*588 * The libelf API is terrible; gelf_update_sym*() takes a data block relative589 * index value, *NOT* the symbol index. As such, iterate the data blocks and590 * adjust index until it fits.591 *592 * If no data block is found, allow adding a new data block provided the index593 * is only one past the end.594 */595static int elf_update_symbol(struct elf *elf, struct section *symtab,596 struct section *symtab_shndx, struct symbol *sym)597{598 Elf32_Word shndx = sym->sec ? sym->sec->idx : SHN_UNDEF;599 Elf_Data *symtab_data = NULL, *shndx_data = NULL;600 Elf64_Xword entsize = symtab->sh.sh_entsize;601 int max_idx, idx = sym->idx;602 Elf_Scn *s, *t = NULL;603 bool is_special_shndx = sym->sym.st_shndx >= SHN_LORESERVE &&604 sym->sym.st_shndx != SHN_XINDEX;605 606 if (is_special_shndx)607 shndx = sym->sym.st_shndx;608 609 s = elf_getscn(elf->elf, symtab->idx);610 if (!s) {611 WARN_ELF("elf_getscn");612 return -1;613 }614 615 if (symtab_shndx) {616 t = elf_getscn(elf->elf, symtab_shndx->idx);617 if (!t) {618 WARN_ELF("elf_getscn");619 return -1;620 }621 }622 623 for (;;) {624 /* get next data descriptor for the relevant sections */625 symtab_data = elf_getdata(s, symtab_data);626 if (t)627 shndx_data = elf_getdata(t, shndx_data);628 629 /* end-of-list */630 if (!symtab_data) {631 /*632 * Over-allocate to avoid O(n^2) symbol creation633 * behaviour. The down side is that libelf doesn't634 * like this; see elf_truncate_section() for the fixup.635 */636 int num = max(1U, sym->idx/3);637 void *buf;638 639 if (idx) {640 /* we don't do holes in symbol tables */641 WARN("index out of range");642 return -1;643 }644 645 /* if @idx == 0, it's the next contiguous entry, create it */646 symtab_data = elf_newdata(s);647 if (t)648 shndx_data = elf_newdata(t);649 650 buf = calloc(num, entsize);651 if (!buf) {652 WARN("malloc");653 return -1;654 }655 656 symtab_data->d_buf = buf;657 symtab_data->d_size = num * entsize;658 symtab_data->d_align = 1;659 symtab_data->d_type = ELF_T_SYM;660 661 mark_sec_changed(elf, symtab, true);662 symtab->truncate = true;663 664 if (t) {665 buf = calloc(num, sizeof(Elf32_Word));666 if (!buf) {667 WARN("malloc");668 return -1;669 }670 671 shndx_data->d_buf = buf;672 shndx_data->d_size = num * sizeof(Elf32_Word);673 shndx_data->d_align = sizeof(Elf32_Word);674 shndx_data->d_type = ELF_T_WORD;675 676 mark_sec_changed(elf, symtab_shndx, true);677 symtab_shndx->truncate = true;678 }679 680 break;681 }682 683 /* empty blocks should not happen */684 if (!symtab_data->d_size) {685 WARN("zero size data");686 return -1;687 }688 689 /* is this the right block? */690 max_idx = symtab_data->d_size / entsize;691 if (idx < max_idx)692 break;693 694 /* adjust index and try again */695 idx -= max_idx;696 }697 698 /* something went side-ways */699 if (idx < 0) {700 WARN("negative index");701 return -1;702 }703 704 /* setup extended section index magic and write the symbol */705 if ((shndx >= SHN_UNDEF && shndx < SHN_LORESERVE) || is_special_shndx) {706 sym->sym.st_shndx = shndx;707 if (!shndx_data)708 shndx = 0;709 } else {710 sym->sym.st_shndx = SHN_XINDEX;711 if (!shndx_data) {712 WARN("no .symtab_shndx");713 return -1;714 }715 }716 717 if (!gelf_update_symshndx(symtab_data, shndx_data, idx, &sym->sym, shndx)) {718 WARN_ELF("gelf_update_symshndx");719 return -1;720 }721 722 return 0;723}724 725static struct symbol *726__elf_create_symbol(struct elf *elf, struct symbol *sym)727{728 struct section *symtab, *symtab_shndx;729 Elf32_Word first_non_local, new_idx;730 struct symbol *old;731 732 symtab = find_section_by_name(elf, ".symtab");733 if (symtab) {734 symtab_shndx = find_section_by_name(elf, ".symtab_shndx");735 } else {736 WARN("no .symtab");737 return NULL;738 }739 740 new_idx = sec_num_entries(symtab);741 742 if (GELF_ST_BIND(sym->sym.st_info) != STB_LOCAL)743 goto non_local;744 745 /*746 * Move the first global symbol, as per sh_info, into a new, higher747 * symbol index. This fees up a spot for a new local symbol.748 */749 first_non_local = symtab->sh.sh_info;750 old = find_symbol_by_index(elf, first_non_local);751 if (old) {752 753 elf_hash_del(symbol, &old->hash, old->idx);754 elf_hash_add(symbol, &old->hash, new_idx);755 old->idx = new_idx;756 757 if (elf_update_symbol(elf, symtab, symtab_shndx, old)) {758 WARN("elf_update_symbol move");759 return NULL;760 }761 762 if (elf_update_sym_relocs(elf, old))763 return NULL;764 765 new_idx = first_non_local;766 }767 768 /*769 * Either way, we will add a LOCAL symbol.770 */771 symtab->sh.sh_info += 1;772 773non_local:774 sym->idx = new_idx;775 if (elf_update_symbol(elf, symtab, symtab_shndx, sym)) {776 WARN("elf_update_symbol");777 return NULL;778 }779 780 symtab->sh.sh_size += symtab->sh.sh_entsize;781 mark_sec_changed(elf, symtab, true);782 783 if (symtab_shndx) {784 symtab_shndx->sh.sh_size += sizeof(Elf32_Word);785 mark_sec_changed(elf, symtab_shndx, true);786 }787 788 return sym;789}790 791static struct symbol *792elf_create_section_symbol(struct elf *elf, struct section *sec)793{794 struct symbol *sym = calloc(1, sizeof(*sym));795 796 if (!sym) {797 perror("malloc");798 return NULL;799 }800 801 sym->name = sec->name;802 sym->sec = sec;803 804 // st_name 0805 sym->sym.st_info = GELF_ST_INFO(STB_LOCAL, STT_SECTION);806 // st_other 0807 // st_value 0808 // st_size 0809 810 sym = __elf_create_symbol(elf, sym);811 if (sym)812 elf_add_symbol(elf, sym);813 814 return sym;815}816 817static int elf_add_string(struct elf *elf, struct section *strtab, char *str);818 819struct symbol *820elf_create_prefix_symbol(struct elf *elf, struct symbol *orig, long size)821{822 struct symbol *sym = calloc(1, sizeof(*sym));823 size_t namelen = strlen(orig->name) + sizeof("__pfx_");824 char *name = malloc(namelen);825 826 if (!sym || !name) {827 perror("malloc");828 return NULL;829 }830 831 snprintf(name, namelen, "__pfx_%s", orig->name);832 833 sym->name = name;834 sym->sec = orig->sec;835 836 sym->sym.st_name = elf_add_string(elf, NULL, name);837 sym->sym.st_info = orig->sym.st_info;838 sym->sym.st_value = orig->sym.st_value - size;839 sym->sym.st_size = size;840 841 sym = __elf_create_symbol(elf, sym);842 if (sym)843 elf_add_symbol(elf, sym);844 845 return sym;846}847 848static struct reloc *elf_init_reloc(struct elf *elf, struct section *rsec,849 unsigned int reloc_idx,850 unsigned long offset, struct symbol *sym,851 s64 addend, unsigned int type)852{853 struct reloc *reloc, empty = { 0 };854 855 if (reloc_idx >= sec_num_entries(rsec)) {856 WARN("%s: bad reloc_idx %u for %s with %d relocs",857 __func__, reloc_idx, rsec->name, sec_num_entries(rsec));858 return NULL;859 }860 861 reloc = &rsec->relocs[reloc_idx];862 863 if (memcmp(reloc, &empty, sizeof(empty))) {864 WARN("%s: %s: reloc %d already initialized!",865 __func__, rsec->name, reloc_idx);866 return NULL;867 }868 869 reloc->sec = rsec;870 reloc->sym = sym;871 872 set_reloc_offset(elf, reloc, offset);873 set_reloc_sym(elf, reloc, sym->idx);874 set_reloc_type(elf, reloc, type);875 set_reloc_addend(elf, reloc, addend);876 877 elf_hash_add(reloc, &reloc->hash, reloc_hash(reloc));878 reloc->sym_next_reloc = sym->relocs;879 sym->relocs = reloc;880 881 return reloc;882}883 884struct reloc *elf_init_reloc_text_sym(struct elf *elf, struct section *sec,885 unsigned long offset,886 unsigned int reloc_idx,887 struct section *insn_sec,888 unsigned long insn_off)889{890 struct symbol *sym = insn_sec->sym;891 int addend = insn_off;892 893 if (!(insn_sec->sh.sh_flags & SHF_EXECINSTR)) {894 WARN("bad call to %s() for data symbol %s",895 __func__, sym->name);896 return NULL;897 }898 899 if (!sym) {900 /*901 * Due to how weak functions work, we must use section based902 * relocations. Symbol based relocations would result in the903 * weak and non-weak function annotations being overlaid on the904 * non-weak function after linking.905 */906 sym = elf_create_section_symbol(elf, insn_sec);907 if (!sym)908 return NULL;909 910 insn_sec->sym = sym;911 }912 913 return elf_init_reloc(elf, sec->rsec, reloc_idx, offset, sym, addend,914 elf_text_rela_type(elf));915}916 917struct reloc *elf_init_reloc_data_sym(struct elf *elf, struct section *sec,918 unsigned long offset,919 unsigned int reloc_idx,920 struct symbol *sym,921 s64 addend)922{923 if (sym->sec && (sec->sh.sh_flags & SHF_EXECINSTR)) {924 WARN("bad call to %s() for text symbol %s",925 __func__, sym->name);926 return NULL;927 }928 929 return elf_init_reloc(elf, sec->rsec, reloc_idx, offset, sym, addend,930 elf_data_rela_type(elf));931}932 933static int read_relocs(struct elf *elf)934{935 unsigned long nr_reloc, max_reloc = 0;936 struct section *rsec;937 struct reloc *reloc;938 unsigned int symndx;939 struct symbol *sym;940 int i;941 942 if (!elf_alloc_hash(reloc, elf->num_relocs))943 return -1;944 945 list_for_each_entry(rsec, &elf->sections, list) {946 if (!is_reloc_sec(rsec))947 continue;948 949 rsec->base = find_section_by_index(elf, rsec->sh.sh_info);950 if (!rsec->base) {951 WARN("can't find base section for reloc section %s",952 rsec->name);953 return -1;954 }955 956 rsec->base->rsec = rsec;957 958 nr_reloc = 0;959 rsec->relocs = calloc(sec_num_entries(rsec), sizeof(*reloc));960 if (!rsec->relocs) {961 perror("calloc");962 return -1;963 }964 for (i = 0; i < sec_num_entries(rsec); i++) {965 reloc = &rsec->relocs[i];966 967 reloc->sec = rsec;968 symndx = reloc_sym(reloc);969 reloc->sym = sym = find_symbol_by_index(elf, symndx);970 if (!reloc->sym) {971 WARN("can't find reloc entry symbol %d for %s",972 symndx, rsec->name);973 return -1;974 }975 976 elf_hash_add(reloc, &reloc->hash, reloc_hash(reloc));977 reloc->sym_next_reloc = sym->relocs;978 sym->relocs = reloc;979 980 nr_reloc++;981 }982 max_reloc = max(max_reloc, nr_reloc);983 }984 985 if (opts.stats) {986 printf("max_reloc: %lu\n", max_reloc);987 printf("num_relocs: %lu\n", elf->num_relocs);988 printf("reloc_bits: %d\n", elf->reloc_bits);989 }990 991 return 0;992}993 994struct elf *elf_open_read(const char *name, int flags)995{996 struct elf *elf;997 Elf_Cmd cmd;998 999 elf_version(EV_CURRENT);1000 1001 elf = malloc(sizeof(*elf));1002 if (!elf) {1003 perror("malloc");1004 return NULL;1005 }1006 memset(elf, 0, sizeof(*elf));1007 1008 INIT_LIST_HEAD(&elf->sections);1009 1010 elf->fd = open(name, flags);1011 if (elf->fd == -1) {1012 fprintf(stderr, "objtool: Can't open '%s': %s\n",1013 name, strerror(errno));1014 goto err;1015 }1016 1017 if ((flags & O_ACCMODE) == O_RDONLY)1018 cmd = ELF_C_READ_MMAP;1019 else if ((flags & O_ACCMODE) == O_RDWR)1020 cmd = ELF_C_RDWR;1021 else /* O_WRONLY */1022 cmd = ELF_C_WRITE;1023 1024 elf->elf = elf_begin(elf->fd, cmd, NULL);1025 if (!elf->elf) {1026 WARN_ELF("elf_begin");1027 goto err;1028 }1029 1030 if (!gelf_getehdr(elf->elf, &elf->ehdr)) {1031 WARN_ELF("gelf_getehdr");1032 goto err;1033 }1034 1035 if (read_sections(elf))1036 goto err;1037 1038 if (read_symbols(elf))1039 goto err;1040 1041 if (read_relocs(elf))1042 goto err;1043 1044 return elf;1045 1046err:1047 elf_close(elf);1048 return NULL;1049}1050 1051static int elf_add_string(struct elf *elf, struct section *strtab, char *str)1052{1053 Elf_Data *data;1054 Elf_Scn *s;1055 int len;1056 1057 if (!strtab)1058 strtab = find_section_by_name(elf, ".strtab");1059 if (!strtab) {1060 WARN("can't find .strtab section");1061 return -1;1062 }1063 1064 s = elf_getscn(elf->elf, strtab->idx);1065 if (!s) {1066 WARN_ELF("elf_getscn");1067 return -1;1068 }1069 1070 data = elf_newdata(s);1071 if (!data) {1072 WARN_ELF("elf_newdata");1073 return -1;1074 }1075 1076 data->d_buf = str;1077 data->d_size = strlen(str) + 1;1078 data->d_align = 1;1079 1080 len = strtab->sh.sh_size;1081 strtab->sh.sh_size += data->d_size;1082 1083 mark_sec_changed(elf, strtab, true);1084 1085 return len;1086}1087 1088struct section *elf_create_section(struct elf *elf, const char *name,1089 size_t entsize, unsigned int nr)1090{1091 struct section *sec, *shstrtab;1092 size_t size = entsize * nr;1093 Elf_Scn *s;1094 1095 sec = malloc(sizeof(*sec));1096 if (!sec) {1097 perror("malloc");1098 return NULL;1099 }1100 memset(sec, 0, sizeof(*sec));1101 1102 INIT_LIST_HEAD(&sec->symbol_list);1103 1104 s = elf_newscn(elf->elf);1105 if (!s) {1106 WARN_ELF("elf_newscn");1107 return NULL;1108 }1109 1110 sec->name = strdup(name);1111 if (!sec->name) {1112 perror("strdup");1113 return NULL;1114 }1115 1116 sec->idx = elf_ndxscn(s);1117 1118 sec->data = elf_newdata(s);1119 if (!sec->data) {1120 WARN_ELF("elf_newdata");1121 return NULL;1122 }1123 1124 sec->data->d_size = size;1125 sec->data->d_align = 1;1126 1127 if (size) {1128 sec->data->d_buf = malloc(size);1129 if (!sec->data->d_buf) {1130 perror("malloc");1131 return NULL;1132 }1133 memset(sec->data->d_buf, 0, size);1134 }1135 1136 if (!gelf_getshdr(s, &sec->sh)) {1137 WARN_ELF("gelf_getshdr");1138 return NULL;1139 }1140 1141 sec->sh.sh_size = size;1142 sec->sh.sh_entsize = entsize;1143 sec->sh.sh_type = SHT_PROGBITS;1144 sec->sh.sh_addralign = 1;1145 sec->sh.sh_flags = SHF_ALLOC;1146 1147 /* Add section name to .shstrtab (or .strtab for Clang) */1148 shstrtab = find_section_by_name(elf, ".shstrtab");1149 if (!shstrtab)1150 shstrtab = find_section_by_name(elf, ".strtab");1151 if (!shstrtab) {1152 WARN("can't find .shstrtab or .strtab section");1153 return NULL;1154 }1155 sec->sh.sh_name = elf_add_string(elf, shstrtab, sec->name);1156 if (sec->sh.sh_name == -1)1157 return NULL;1158 1159 list_add_tail(&sec->list, &elf->sections);1160 elf_hash_add(section, &sec->hash, sec->idx);1161 elf_hash_add(section_name, &sec->name_hash, str_hash(sec->name));1162 1163 mark_sec_changed(elf, sec, true);1164 1165 return sec;1166}1167 1168static struct section *elf_create_rela_section(struct elf *elf,1169 struct section *sec,1170 unsigned int reloc_nr)1171{1172 struct section *rsec;1173 char *rsec_name;1174 1175 rsec_name = malloc(strlen(sec->name) + strlen(".rela") + 1);1176 if (!rsec_name) {1177 perror("malloc");1178 return NULL;1179 }1180 strcpy(rsec_name, ".rela");1181 strcat(rsec_name, sec->name);1182 1183 rsec = elf_create_section(elf, rsec_name, elf_rela_size(elf), reloc_nr);1184 free(rsec_name);1185 if (!rsec)1186 return NULL;1187 1188 rsec->data->d_type = ELF_T_RELA;1189 rsec->sh.sh_type = SHT_RELA;1190 rsec->sh.sh_addralign = elf_addr_size(elf);1191 rsec->sh.sh_link = find_section_by_name(elf, ".symtab")->idx;1192 rsec->sh.sh_info = sec->idx;1193 rsec->sh.sh_flags = SHF_INFO_LINK;1194 1195 rsec->relocs = calloc(sec_num_entries(rsec), sizeof(struct reloc));1196 if (!rsec->relocs) {1197 perror("calloc");1198 return NULL;1199 }1200 1201 sec->rsec = rsec;1202 rsec->base = sec;1203 1204 return rsec;1205}1206 1207struct section *elf_create_section_pair(struct elf *elf, const char *name,1208 size_t entsize, unsigned int nr,1209 unsigned int reloc_nr)1210{1211 struct section *sec;1212 1213 sec = elf_create_section(elf, name, entsize, nr);1214 if (!sec)1215 return NULL;1216 1217 if (!elf_create_rela_section(elf, sec, reloc_nr))1218 return NULL;1219 1220 return sec;1221}1222 1223int elf_write_insn(struct elf *elf, struct section *sec,1224 unsigned long offset, unsigned int len,1225 const char *insn)1226{1227 Elf_Data *data = sec->data;1228 1229 if (data->d_type != ELF_T_BYTE || data->d_off) {1230 WARN("write to unexpected data for section: %s", sec->name);1231 return -1;1232 }1233 1234 memcpy(data->d_buf + offset, insn, len);1235 1236 mark_sec_changed(elf, sec, true);1237 1238 return 0;1239}1240 1241/*1242 * When Elf_Scn::sh_size is smaller than the combined Elf_Data::d_size1243 * do you:1244 *1245 * A) adhere to the section header and truncate the data, or1246 * B) ignore the section header and write out all the data you've got?1247 *1248 * Yes, libelf sucks and we need to manually truncate if we over-allocate data.1249 */1250static int elf_truncate_section(struct elf *elf, struct section *sec)1251{1252 u64 size = sec->sh.sh_size;1253 bool truncated = false;1254 Elf_Data *data = NULL;1255 Elf_Scn *s;1256 1257 s = elf_getscn(elf->elf, sec->idx);1258 if (!s) {1259 WARN_ELF("elf_getscn");1260 return -1;1261 }1262 1263 for (;;) {1264 /* get next data descriptor for the relevant section */1265 data = elf_getdata(s, data);1266 1267 if (!data) {1268 if (size) {1269 WARN("end of section data but non-zero size left\n");1270 return -1;1271 }1272 return 0;1273 }1274 1275 if (truncated) {1276 /* when we remove symbols */1277 WARN("truncated; but more data\n");1278 return -1;1279 }1280 1281 if (!data->d_size) {1282 WARN("zero size data");1283 return -1;1284 }1285 1286 if (data->d_size > size) {1287 truncated = true;1288 data->d_size = size;1289 }1290 1291 size -= data->d_size;1292 }1293}1294 1295int elf_write(struct elf *elf)1296{1297 struct section *sec;1298 Elf_Scn *s;1299 1300 if (opts.dryrun)1301 return 0;1302 1303 /* Update changed relocation sections and section headers: */1304 list_for_each_entry(sec, &elf->sections, list) {1305 if (sec->truncate)1306 elf_truncate_section(elf, sec);1307 1308 if (sec_changed(sec)) {1309 s = elf_getscn(elf->elf, sec->idx);1310 if (!s) {1311 WARN_ELF("elf_getscn");1312 return -1;1313 }1314 1315 /* Note this also flags the section dirty */1316 if (!gelf_update_shdr(s, &sec->sh)) {1317 WARN_ELF("gelf_update_shdr");1318 return -1;1319 }1320 1321 mark_sec_changed(elf, sec, false);1322 }1323 }1324 1325 /* Make sure the new section header entries get updated properly. */1326 elf_flagelf(elf->elf, ELF_C_SET, ELF_F_DIRTY);1327 1328 /* Write all changes to the file. */1329 if (elf_update(elf->elf, ELF_C_WRITE) < 0) {1330 WARN_ELF("elf_update");1331 return -1;1332 }1333 1334 elf->changed = false;1335 1336 return 0;1337}1338 1339void elf_close(struct elf *elf)1340{1341 if (elf->elf)1342 elf_end(elf->elf);1343 1344 if (elf->fd > 0)1345 close(elf->fd);1346 1347 /*1348 * NOTE: All remaining allocations are leaked on purpose. Objtool is1349 * about to exit anyway.1350 */1351}1352