2 * elf.c - ELF access library
4 * Adapted from kpatch (https://github.com/dynup/kpatch):
5 * Copyright (C) 2013-2015 Josh Poimboeuf <jpoimboe@redhat.com>
6 * Copyright (C) 2014 Seth Jennings <sjenning@redhat.com>
8 * This program is free software; you can redistribute it and/or
9 * modify it under the terms of the GNU General Public License
10 * as published by the Free Software Foundation; either version 2
11 * of the License, or (at your option) any later version.
13 * This program is distributed in the hope that it will be useful,
14 * but WITHOUT ANY WARRANTY; without even the implied warranty of
15 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
16 * GNU General Public License for more details.
18 * You should have received a copy of the GNU General Public License
19 * along with this program; if not, see <http://www.gnu.org/licenses/>.
22 #include <sys/types.h>
34 #define MAX_NAME_LEN 128
36 struct section *find_section_by_name(struct elf *elf, const char *name)
40 list_for_each_entry(sec, &elf->sections, list)
41 if (!strcmp(sec->name, name))
47 static struct section *find_section_by_index(struct elf *elf,
52 list_for_each_entry(sec, &elf->sections, list)
59 static struct symbol *find_symbol_by_index(struct elf *elf, unsigned int idx)
64 list_for_each_entry(sec, &elf->sections, list)
65 hash_for_each_possible(sec->symbol_hash, sym, hash, idx)
72 struct symbol *find_symbol_by_offset(struct section *sec, unsigned long offset)
76 list_for_each_entry(sym, &sec->symbol_list, list)
77 if (sym->type != STT_SECTION &&
78 sym->offset == offset)
84 struct symbol *find_symbol_by_name(struct elf *elf, const char *name)
89 list_for_each_entry(sec, &elf->sections, list)
90 list_for_each_entry(sym, &sec->symbol_list, list)
91 if (!strcmp(sym->name, name))
97 struct symbol *find_symbol_containing(struct section *sec, unsigned long offset)
101 list_for_each_entry(sym, &sec->symbol_list, list)
102 if (sym->type != STT_SECTION &&
103 offset >= sym->offset && offset < sym->offset + sym->len)
109 struct rela *find_rela_by_dest_range(struct section *sec, unsigned long offset,
118 for (o = offset; o < offset + len; o++)
119 hash_for_each_possible(sec->rela->rela_hash, rela, hash, o)
120 if (rela->offset == o)
126 struct rela *find_rela_by_dest(struct section *sec, unsigned long offset)
128 return find_rela_by_dest_range(sec, offset, 1);
131 struct symbol *find_containing_func(struct section *sec, unsigned long offset)
135 list_for_each_entry(func, &sec->symbol_list, list)
136 if (func->type == STT_FUNC && offset >= func->offset &&
137 offset < func->offset + func->len)
143 static int read_sections(struct elf *elf)
147 size_t shstrndx, sections_nr;
150 if (elf_getshdrnum(elf->elf, §ions_nr)) {
151 WARN_ELF("elf_getshdrnum");
155 if (elf_getshdrstrndx(elf->elf, &shstrndx)) {
156 WARN_ELF("elf_getshdrstrndx");
160 for (i = 0; i < sections_nr; i++) {
161 sec = malloc(sizeof(*sec));
166 memset(sec, 0, sizeof(*sec));
168 INIT_LIST_HEAD(&sec->symbol_list);
169 INIT_LIST_HEAD(&sec->rela_list);
170 hash_init(sec->rela_hash);
171 hash_init(sec->symbol_hash);
173 list_add_tail(&sec->list, &elf->sections);
175 s = elf_getscn(elf->elf, i);
177 WARN_ELF("elf_getscn");
181 sec->idx = elf_ndxscn(s);
183 if (!gelf_getshdr(s, &sec->sh)) {
184 WARN_ELF("gelf_getshdr");
188 sec->name = elf_strptr(elf->elf, shstrndx, sec->sh.sh_name);
190 WARN_ELF("elf_strptr");
194 if (sec->sh.sh_size != 0) {
195 sec->data = elf_getdata(s, NULL);
197 WARN_ELF("elf_getdata");
200 if (sec->data->d_off != 0 ||
201 sec->data->d_size != sec->sh.sh_size) {
202 WARN("unexpected data attributes for %s",
207 sec->len = sec->sh.sh_size;
210 /* sanity check, one more call to elf_nextscn() should return NULL */
211 if (elf_nextscn(elf->elf, s)) {
212 WARN("section entry mismatch");
219 static int read_symbols(struct elf *elf)
221 struct section *symtab, *sec;
222 struct symbol *sym, *pfunc, *alias;
223 struct list_head *entry, *tmp;
227 symtab = find_section_by_name(elf, ".symtab");
229 WARN("missing symbol table");
233 symbols_nr = symtab->sh.sh_size / symtab->sh.sh_entsize;
235 for (i = 0; i < symbols_nr; i++) {
236 sym = malloc(sizeof(*sym));
241 memset(sym, 0, sizeof(*sym));
246 if (!gelf_getsym(symtab->data, i, &sym->sym)) {
247 WARN_ELF("gelf_getsym");
251 sym->name = elf_strptr(elf->elf, symtab->sh.sh_link,
254 WARN_ELF("elf_strptr");
258 sym->type = GELF_ST_TYPE(sym->sym.st_info);
259 sym->bind = GELF_ST_BIND(sym->sym.st_info);
261 if (sym->sym.st_shndx > SHN_UNDEF &&
262 sym->sym.st_shndx < SHN_LORESERVE) {
263 sym->sec = find_section_by_index(elf,
266 WARN("couldn't find section for symbol %s",
270 if (sym->type == STT_SECTION) {
271 sym->name = sym->sec->name;
275 sym->sec = find_section_by_index(elf, 0);
277 sym->offset = sym->sym.st_value;
278 sym->len = sym->sym.st_size;
280 /* sorted insert into a per-section list */
281 entry = &sym->sec->symbol_list;
282 list_for_each_prev(tmp, &sym->sec->symbol_list) {
285 s = list_entry(tmp, struct symbol, list);
287 if (sym->offset > s->offset) {
292 if (sym->offset == s->offset) {
293 if (sym->len == s->len && alias == sym)
296 if (sym->len >= s->len) {
303 list_add(&sym->list, entry);
304 hash_add(sym->sec->symbol_hash, &sym->hash, sym->idx);
307 /* Create parent/child links for any cold subfunctions */
308 list_for_each_entry(sec, &elf->sections, list) {
309 list_for_each_entry(sym, &sec->symbol_list, list) {
310 char pname[MAX_NAME_LEN + 1];
312 if (sym->type != STT_FUNC)
314 sym->pfunc = sym->cfunc = sym;
315 coldstr = strstr(sym->name, ".cold");
319 pnamelen = coldstr - sym->name;
320 if (pnamelen > MAX_NAME_LEN) {
321 WARN("%s(): parent function name exceeds maximum length of %d characters",
322 sym->name, MAX_NAME_LEN);
326 strncpy(pname, sym->name, pnamelen);
327 pname[pnamelen] = '\0';
328 pfunc = find_symbol_by_name(elf, pname);
331 WARN("%s(): can't find parent function",
340 * Unfortunately, -fnoreorder-functions puts the child
341 * inside the parent. Remove the overlap so we can
342 * have sane assumptions.
344 * Note that pfunc->len now no longer matches
345 * pfunc->sym.st_size.
347 if (sym->sec == pfunc->sec &&
348 sym->offset >= pfunc->offset &&
349 sym->offset + sym->len == pfunc->offset + pfunc->len) {
350 pfunc->len -= sym->len;
362 static int read_relas(struct elf *elf)
369 list_for_each_entry(sec, &elf->sections, list) {
370 if (sec->sh.sh_type != SHT_RELA)
373 sec->base = find_section_by_name(elf, sec->name + 5);
375 WARN("can't find base section for rela section %s",
380 sec->base->rela = sec;
382 for (i = 0; i < sec->sh.sh_size / sec->sh.sh_entsize; i++) {
383 rela = malloc(sizeof(*rela));
388 memset(rela, 0, sizeof(*rela));
390 if (!gelf_getrela(sec->data, i, &rela->rela)) {
391 WARN_ELF("gelf_getrela");
395 rela->type = GELF_R_TYPE(rela->rela.r_info);
396 rela->addend = rela->rela.r_addend;
397 rela->offset = rela->rela.r_offset;
398 symndx = GELF_R_SYM(rela->rela.r_info);
399 rela->sym = find_symbol_by_index(elf, symndx);
400 rela->rela_sec = sec;
402 WARN("can't find rela entry symbol %d for %s",
407 list_add_tail(&rela->list, &sec->rela_list);
408 hash_add(sec->rela_hash, &rela->hash, rela->offset);
416 struct elf *elf_open(const char *name, int flags)
421 elf_version(EV_CURRENT);
423 elf = malloc(sizeof(*elf));
428 memset(elf, 0, sizeof(*elf));
430 INIT_LIST_HEAD(&elf->sections);
432 elf->fd = open(name, flags);
434 fprintf(stderr, "objtool: Can't open '%s': %s\n",
435 name, strerror(errno));
439 if ((flags & O_ACCMODE) == O_RDONLY)
440 cmd = ELF_C_READ_MMAP;
441 else if ((flags & O_ACCMODE) == O_RDWR)
446 elf->elf = elf_begin(elf->fd, cmd, NULL);
448 WARN_ELF("elf_begin");
452 if (!gelf_getehdr(elf->elf, &elf->ehdr)) {
453 WARN_ELF("gelf_getehdr");
457 if (read_sections(elf))
460 if (read_symbols(elf))
473 struct section *elf_create_section(struct elf *elf, const char *name,
474 size_t entsize, int nr)
476 struct section *sec, *shstrtab;
477 size_t size = entsize * nr;
481 sec = malloc(sizeof(*sec));
486 memset(sec, 0, sizeof(*sec));
488 INIT_LIST_HEAD(&sec->symbol_list);
489 INIT_LIST_HEAD(&sec->rela_list);
490 hash_init(sec->rela_hash);
491 hash_init(sec->symbol_hash);
493 list_add_tail(&sec->list, &elf->sections);
495 s = elf_newscn(elf->elf);
497 WARN_ELF("elf_newscn");
501 sec->name = strdup(name);
507 sec->idx = elf_ndxscn(s);
511 sec->data = elf_newdata(s);
513 WARN_ELF("elf_newdata");
517 sec->data->d_size = size;
518 sec->data->d_align = 1;
521 sec->data->d_buf = malloc(size);
522 if (!sec->data->d_buf) {
526 memset(sec->data->d_buf, 0, size);
529 if (!gelf_getshdr(s, &sec->sh)) {
530 WARN_ELF("gelf_getshdr");
534 sec->sh.sh_size = size;
535 sec->sh.sh_entsize = entsize;
536 sec->sh.sh_type = SHT_PROGBITS;
537 sec->sh.sh_addralign = 1;
538 sec->sh.sh_flags = SHF_ALLOC;
541 /* Add section name to .shstrtab (or .strtab for Clang) */
542 shstrtab = find_section_by_name(elf, ".shstrtab");
544 shstrtab = find_section_by_name(elf, ".strtab");
546 WARN("can't find .shstrtab or .strtab section");
550 s = elf_getscn(elf->elf, shstrtab->idx);
552 WARN_ELF("elf_getscn");
556 data = elf_newdata(s);
558 WARN_ELF("elf_newdata");
562 data->d_buf = sec->name;
563 data->d_size = strlen(name) + 1;
566 sec->sh.sh_name = shstrtab->len;
568 shstrtab->len += strlen(name) + 1;
569 shstrtab->changed = true;
574 struct section *elf_create_rela_section(struct elf *elf, struct section *base)
579 relaname = malloc(strlen(base->name) + strlen(".rela") + 1);
584 strcpy(relaname, ".rela");
585 strcat(relaname, base->name);
587 sec = elf_create_section(elf, relaname, sizeof(GElf_Rela), 0);
595 sec->sh.sh_type = SHT_RELA;
596 sec->sh.sh_addralign = 8;
597 sec->sh.sh_link = find_section_by_name(elf, ".symtab")->idx;
598 sec->sh.sh_info = base->idx;
599 sec->sh.sh_flags = SHF_INFO_LINK;
604 int elf_rebuild_rela_section(struct section *sec)
607 int nr, idx = 0, size;
611 list_for_each_entry(rela, &sec->rela_list, list)
614 size = nr * sizeof(*relas);
615 relas = malloc(size);
621 sec->data->d_buf = relas;
622 sec->data->d_size = size;
624 sec->sh.sh_size = size;
627 list_for_each_entry(rela, &sec->rela_list, list) {
628 relas[idx].r_offset = rela->offset;
629 relas[idx].r_addend = rela->addend;
630 relas[idx].r_info = GELF_R_INFO(rela->sym->idx, rela->type);
637 int elf_write(struct elf *elf)
642 /* Update section headers for changed sections: */
643 list_for_each_entry(sec, &elf->sections, list) {
645 s = elf_getscn(elf->elf, sec->idx);
647 WARN_ELF("elf_getscn");
650 if (!gelf_update_shdr(s, &sec->sh)) {
651 WARN_ELF("gelf_update_shdr");
657 /* Make sure the new section header entries get updated properly. */
658 elf_flagelf(elf->elf, ELF_C_SET, ELF_F_DIRTY);
660 /* Write all changes to the file. */
661 if (elf_update(elf->elf, ELF_C_WRITE) < 0) {
662 WARN_ELF("elf_update");
669 void elf_close(struct elf *elf)
671 struct section *sec, *tmpsec;
672 struct symbol *sym, *tmpsym;
673 struct rela *rela, *tmprela;
681 list_for_each_entry_safe(sec, tmpsec, &elf->sections, list) {
682 list_for_each_entry_safe(sym, tmpsym, &sec->symbol_list, list) {
683 list_del(&sym->list);
684 hash_del(&sym->hash);
687 list_for_each_entry_safe(rela, tmprela, &sec->rela_list, list) {
688 list_del(&rela->list);
689 hash_del(&rela->hash);
692 list_del(&sec->list);