1 // SPDX-License-Identifier: GPL-2.0-or-later
3 * elf.c - ELF access library
5 * Adapted from kpatch (https://github.com/dynup/kpatch):
10 #include <sys/types.h>
19 #include <linux/interval_tree_generic.h>
20 #include <objtool/builtin.h>
22 #include <objtool/elf.h>
23 #include <objtool/warn.h>
25 #define MAX_NAME_LEN 128
27 static inline u32 str_hash(const char *str)
29 return jhash(str, strlen(str), 0);
32 #define __elf_table(name) (elf->name##_hash)
33 #define __elf_bits(name) (elf->name##_bits)
35 #define elf_hash_add(name, node, key) \
36 hlist_add_head(node, &__elf_table(name)[hash_min(key, __elf_bits(name))])
38 #define elf_hash_for_each_possible(name, obj, member, key) \
39 hlist_for_each_entry(obj, &__elf_table(name)[hash_min(key, __elf_bits(name))], member)
41 #define elf_alloc_hash(name, size) \
43 __elf_bits(name) = max(10, ilog2(size)); \
44 __elf_table(name) = mmap(NULL, sizeof(struct hlist_head) << __elf_bits(name), \
45 PROT_READ|PROT_WRITE, \
46 MAP_PRIVATE|MAP_ANON, -1, 0); \
47 if (__elf_table(name) == (void *)-1L) { \
48 WARN("mmap fail " #name); \
49 __elf_table(name) = NULL; \
54 static inline unsigned long __sym_start(struct symbol *s)
59 static inline unsigned long __sym_last(struct symbol *s)
61 return s->offset + s->len - 1;
64 INTERVAL_TREE_DEFINE(struct symbol, node, unsigned long, __subtree_last,
65 __sym_start, __sym_last, static, __sym)
67 #define __sym_for_each(_iter, _tree, _start, _end) \
68 for (_iter = __sym_iter_first((_tree), (_start), (_end)); \
69 _iter; _iter = __sym_iter_next(_iter, (_start), (_end)))
73 const struct symbol *sym;
77 * Find !section symbol where @offset is after it.
79 static int symbol_hole_by_offset(const void *key, const struct rb_node *node)
81 const struct symbol *s = rb_entry(node, struct symbol, node);
82 struct symbol_hole *sh = (void *)key;
84 if (sh->key < s->offset)
87 if (sh->key >= s->offset + s->len) {
88 if (s->type != STT_SECTION)
96 struct section *find_section_by_name(const struct elf *elf, const char *name)
100 elf_hash_for_each_possible(section_name, sec, name_hash, str_hash(name)) {
101 if (!strcmp(sec->name, name))
108 static struct section *find_section_by_index(struct elf *elf,
113 elf_hash_for_each_possible(section, sec, hash, idx) {
121 static struct symbol *find_symbol_by_index(struct elf *elf, unsigned int idx)
125 elf_hash_for_each_possible(symbol, sym, hash, idx) {
133 struct symbol *find_symbol_by_offset(struct section *sec, unsigned long offset)
135 struct rb_root_cached *tree = (struct rb_root_cached *)&sec->symbol_tree;
138 __sym_for_each(iter, tree, offset, offset) {
139 if (iter->offset == offset && iter->type != STT_SECTION)
146 struct symbol *find_func_by_offset(struct section *sec, unsigned long offset)
148 struct rb_root_cached *tree = (struct rb_root_cached *)&sec->symbol_tree;
151 __sym_for_each(iter, tree, offset, offset) {
152 if (iter->offset == offset && iter->type == STT_FUNC)
159 struct symbol *find_symbol_containing(const struct section *sec, unsigned long offset)
161 struct rb_root_cached *tree = (struct rb_root_cached *)&sec->symbol_tree;
164 __sym_for_each(iter, tree, offset, offset) {
165 if (iter->type != STT_SECTION)
173 * Returns size of hole starting at @offset.
175 int find_symbol_hole_containing(const struct section *sec, unsigned long offset)
177 struct symbol_hole hole = {
185 * Find the rightmost symbol for which @offset is after it.
187 n = rb_find(&hole, &sec->symbol_tree.rb_root, symbol_hole_by_offset);
189 /* found a symbol that contains @offset */
191 return 0; /* not a hole */
193 /* didn't find a symbol for which @offset is after it */
195 return 0; /* not a hole */
197 /* @offset >= sym->offset + sym->len, find symbol after it */
198 n = rb_next(&hole.sym->node);
200 return -1; /* until end of address space */
202 /* hole until start of next symbol */
203 s = rb_entry(n, struct symbol, node);
204 return s->offset - offset;
207 struct symbol *find_func_containing(struct section *sec, unsigned long offset)
209 struct rb_root_cached *tree = (struct rb_root_cached *)&sec->symbol_tree;
212 __sym_for_each(iter, tree, offset, offset) {
213 if (iter->type == STT_FUNC)
220 struct symbol *find_symbol_by_name(const struct elf *elf, const char *name)
224 elf_hash_for_each_possible(symbol_name, sym, name_hash, str_hash(name)) {
225 if (!strcmp(sym->name, name))
232 struct reloc *find_reloc_by_dest_range(const struct elf *elf, struct section *sec,
233 unsigned long offset, unsigned int len)
235 struct reloc *reloc, *r = NULL;
243 for_offset_range(o, offset, offset + len) {
244 elf_hash_for_each_possible(reloc, reloc, hash,
245 sec_offset_hash(sec, o)) {
246 if (reloc->sec != sec)
249 if (reloc->offset >= offset && reloc->offset < offset + len) {
250 if (!r || reloc->offset < r->offset)
261 struct reloc *find_reloc_by_dest(const struct elf *elf, struct section *sec, unsigned long offset)
263 return find_reloc_by_dest_range(elf, sec, offset, 1);
266 static int read_sections(struct elf *elf)
270 size_t shstrndx, sections_nr;
273 if (elf_getshdrnum(elf->elf, §ions_nr)) {
274 WARN_ELF("elf_getshdrnum");
278 if (elf_getshdrstrndx(elf->elf, &shstrndx)) {
279 WARN_ELF("elf_getshdrstrndx");
283 if (!elf_alloc_hash(section, sections_nr) ||
284 !elf_alloc_hash(section_name, sections_nr))
287 for (i = 0; i < sections_nr; i++) {
288 sec = malloc(sizeof(*sec));
293 memset(sec, 0, sizeof(*sec));
295 INIT_LIST_HEAD(&sec->symbol_list);
296 INIT_LIST_HEAD(&sec->reloc_list);
298 s = elf_getscn(elf->elf, i);
300 WARN_ELF("elf_getscn");
304 sec->idx = elf_ndxscn(s);
306 if (!gelf_getshdr(s, &sec->sh)) {
307 WARN_ELF("gelf_getshdr");
311 sec->name = elf_strptr(elf->elf, shstrndx, sec->sh.sh_name);
313 WARN_ELF("elf_strptr");
317 if (sec->sh.sh_size != 0) {
318 sec->data = elf_getdata(s, NULL);
320 WARN_ELF("elf_getdata");
323 if (sec->data->d_off != 0 ||
324 sec->data->d_size != sec->sh.sh_size) {
325 WARN("unexpected data attributes for %s",
331 if (sec->sh.sh_flags & SHF_EXECINSTR)
332 elf->text_size += sec->sh.sh_size;
334 list_add_tail(&sec->list, &elf->sections);
335 elf_hash_add(section, &sec->hash, sec->idx);
336 elf_hash_add(section_name, &sec->name_hash, str_hash(sec->name));
340 printf("nr_sections: %lu\n", (unsigned long)sections_nr);
341 printf("section_bits: %d\n", elf->section_bits);
344 /* sanity check, one more call to elf_nextscn() should return NULL */
345 if (elf_nextscn(elf->elf, s)) {
346 WARN("section entry mismatch");
353 static void elf_add_symbol(struct elf *elf, struct symbol *sym)
355 struct list_head *entry;
356 struct rb_node *pnode;
359 INIT_LIST_HEAD(&sym->reloc_list);
360 INIT_LIST_HEAD(&sym->pv_target);
363 sym->type = GELF_ST_TYPE(sym->sym.st_info);
364 sym->bind = GELF_ST_BIND(sym->sym.st_info);
366 if (sym->type == STT_FILE)
369 sym->offset = sym->sym.st_value;
370 sym->len = sym->sym.st_size;
372 __sym_for_each(iter, &sym->sec->symbol_tree, sym->offset, sym->offset) {
373 if (iter->offset == sym->offset && iter->type == sym->type)
377 __sym_insert(sym, &sym->sec->symbol_tree);
378 pnode = rb_prev(&sym->node);
380 entry = &rb_entry(pnode, struct symbol, node)->list;
382 entry = &sym->sec->symbol_list;
383 list_add(&sym->list, entry);
384 elf_hash_add(symbol, &sym->hash, sym->idx);
385 elf_hash_add(symbol_name, &sym->name_hash, str_hash(sym->name));
388 * Don't store empty STT_NOTYPE symbols in the rbtree. They
389 * can exist within a function, confusing the sorting.
392 __sym_remove(sym, &sym->sec->symbol_tree);
395 static int read_symbols(struct elf *elf)
397 struct section *symtab, *symtab_shndx, *sec;
398 struct symbol *sym, *pfunc;
401 Elf_Data *shndx_data = NULL;
404 symtab = find_section_by_name(elf, ".symtab");
406 symtab_shndx = find_section_by_name(elf, ".symtab_shndx");
408 shndx_data = symtab_shndx->data;
410 symbols_nr = symtab->sh.sh_size / symtab->sh.sh_entsize;
413 * A missing symbol table is actually possible if it's an empty
414 * .o file. This can happen for thunk_64.o. Make sure to at
415 * least allocate the symbol hash tables so we can do symbol
416 * lookups without crashing.
421 if (!elf_alloc_hash(symbol, symbols_nr) ||
422 !elf_alloc_hash(symbol_name, symbols_nr))
425 for (i = 0; i < symbols_nr; i++) {
426 sym = malloc(sizeof(*sym));
431 memset(sym, 0, sizeof(*sym));
435 if (!gelf_getsymshndx(symtab->data, shndx_data, i, &sym->sym,
437 WARN_ELF("gelf_getsymshndx");
441 sym->name = elf_strptr(elf->elf, symtab->sh.sh_link,
444 WARN_ELF("elf_strptr");
448 if ((sym->sym.st_shndx > SHN_UNDEF &&
449 sym->sym.st_shndx < SHN_LORESERVE) ||
450 (shndx_data && sym->sym.st_shndx == SHN_XINDEX)) {
451 if (sym->sym.st_shndx != SHN_XINDEX)
452 shndx = sym->sym.st_shndx;
454 sym->sec = find_section_by_index(elf, shndx);
456 WARN("couldn't find section for symbol %s",
460 if (GELF_ST_TYPE(sym->sym.st_info) == STT_SECTION) {
461 sym->name = sym->sec->name;
465 sym->sec = find_section_by_index(elf, 0);
467 elf_add_symbol(elf, sym);
471 printf("nr_symbols: %lu\n", (unsigned long)symbols_nr);
472 printf("symbol_bits: %d\n", elf->symbol_bits);
475 /* Create parent/child links for any cold subfunctions */
476 list_for_each_entry(sec, &elf->sections, list) {
477 list_for_each_entry(sym, &sec->symbol_list, list) {
478 char pname[MAX_NAME_LEN + 1];
480 if (sym->type != STT_FUNC)
483 if (sym->pfunc == NULL)
486 if (sym->cfunc == NULL)
489 coldstr = strstr(sym->name, ".cold");
493 pnamelen = coldstr - sym->name;
494 if (pnamelen > MAX_NAME_LEN) {
495 WARN("%s(): parent function name exceeds maximum length of %d characters",
496 sym->name, MAX_NAME_LEN);
500 strncpy(pname, sym->name, pnamelen);
501 pname[pnamelen] = '\0';
502 pfunc = find_symbol_by_name(elf, pname);
505 WARN("%s(): can't find parent function",
514 * Unfortunately, -fnoreorder-functions puts the child
515 * inside the parent. Remove the overlap so we can
516 * have sane assumptions.
518 * Note that pfunc->len now no longer matches
519 * pfunc->sym.st_size.
521 if (sym->sec == pfunc->sec &&
522 sym->offset >= pfunc->offset &&
523 sym->offset + sym->len == pfunc->offset + pfunc->len) {
524 pfunc->len -= sym->len;
536 static struct section *elf_create_reloc_section(struct elf *elf,
537 struct section *base,
540 int elf_add_reloc(struct elf *elf, struct section *sec, unsigned long offset,
541 unsigned int type, struct symbol *sym, s64 addend)
545 if (!sec->reloc && !elf_create_reloc_section(elf, sec, SHT_RELA))
548 reloc = malloc(sizeof(*reloc));
553 memset(reloc, 0, sizeof(*reloc));
555 reloc->sec = sec->reloc;
556 reloc->offset = offset;
559 reloc->addend = addend;
561 list_add_tail(&reloc->sym_reloc_entry, &sym->reloc_list);
562 list_add_tail(&reloc->list, &sec->reloc->reloc_list);
563 elf_hash_add(reloc, &reloc->hash, reloc_hash(reloc));
565 sec->reloc->sh.sh_size += sec->reloc->sh.sh_entsize;
566 sec->reloc->changed = true;
572 * Ensure that any reloc section containing references to @sym is marked
573 * changed such that it will get re-generated in elf_rebuild_reloc_sections()
574 * with the new symbol index.
576 static void elf_dirty_reloc_sym(struct elf *elf, struct symbol *sym)
580 list_for_each_entry(reloc, &sym->reloc_list, sym_reloc_entry)
581 reloc->sec->changed = true;
585 * The libelf API is terrible; gelf_update_sym*() takes a data block relative
586 * index value, *NOT* the symbol index. As such, iterate the data blocks and
587 * adjust index until it fits.
589 * If no data block is found, allow adding a new data block provided the index
590 * is only one past the end.
592 static int elf_update_symbol(struct elf *elf, struct section *symtab,
593 struct section *symtab_shndx, struct symbol *sym)
595 Elf32_Word shndx = sym->sec ? sym->sec->idx : SHN_UNDEF;
596 Elf_Data *symtab_data = NULL, *shndx_data = NULL;
597 Elf64_Xword entsize = symtab->sh.sh_entsize;
598 int max_idx, idx = sym->idx;
599 Elf_Scn *s, *t = NULL;
600 bool is_special_shndx = sym->sym.st_shndx >= SHN_LORESERVE &&
601 sym->sym.st_shndx != SHN_XINDEX;
603 if (is_special_shndx)
604 shndx = sym->sym.st_shndx;
606 s = elf_getscn(elf->elf, symtab->idx);
608 WARN_ELF("elf_getscn");
613 t = elf_getscn(elf->elf, symtab_shndx->idx);
615 WARN_ELF("elf_getscn");
621 /* get next data descriptor for the relevant sections */
622 symtab_data = elf_getdata(s, symtab_data);
624 shndx_data = elf_getdata(t, shndx_data);
629 * Over-allocate to avoid O(n^2) symbol creation
630 * behaviour. The down side is that libelf doesn't
631 * like this; see elf_truncate_section() for the fixup.
633 int num = max(1U, sym->idx/3);
637 /* we don't do holes in symbol tables */
638 WARN("index out of range");
642 /* if @idx == 0, it's the next contiguous entry, create it */
643 symtab_data = elf_newdata(s);
645 shndx_data = elf_newdata(t);
647 buf = calloc(num, entsize);
653 symtab_data->d_buf = buf;
654 symtab_data->d_size = num * entsize;
655 symtab_data->d_align = 1;
656 symtab_data->d_type = ELF_T_SYM;
658 symtab->changed = true;
659 symtab->truncate = true;
662 buf = calloc(num, sizeof(Elf32_Word));
668 shndx_data->d_buf = buf;
669 shndx_data->d_size = num * sizeof(Elf32_Word);
670 shndx_data->d_align = sizeof(Elf32_Word);
671 shndx_data->d_type = ELF_T_WORD;
673 symtab_shndx->changed = true;
674 symtab_shndx->truncate = true;
680 /* empty blocks should not happen */
681 if (!symtab_data->d_size) {
682 WARN("zero size data");
686 /* is this the right block? */
687 max_idx = symtab_data->d_size / entsize;
691 /* adjust index and try again */
695 /* something went side-ways */
697 WARN("negative index");
701 /* setup extended section index magic and write the symbol */
702 if ((shndx >= SHN_UNDEF && shndx < SHN_LORESERVE) || is_special_shndx) {
703 sym->sym.st_shndx = shndx;
707 sym->sym.st_shndx = SHN_XINDEX;
709 WARN("no .symtab_shndx");
714 if (!gelf_update_symshndx(symtab_data, shndx_data, idx, &sym->sym, shndx)) {
715 WARN_ELF("gelf_update_symshndx");
722 static struct symbol *
723 __elf_create_symbol(struct elf *elf, struct symbol *sym)
725 struct section *symtab, *symtab_shndx;
726 Elf32_Word first_non_local, new_idx;
729 symtab = find_section_by_name(elf, ".symtab");
731 symtab_shndx = find_section_by_name(elf, ".symtab_shndx");
737 new_idx = symtab->sh.sh_size / symtab->sh.sh_entsize;
739 if (GELF_ST_BIND(sym->sym.st_info) != STB_LOCAL)
743 * Move the first global symbol, as per sh_info, into a new, higher
744 * symbol index. This fees up a spot for a new local symbol.
746 first_non_local = symtab->sh.sh_info;
747 old = find_symbol_by_index(elf, first_non_local);
751 hlist_del(&old->hash);
752 elf_hash_add(symbol, &old->hash, old->idx);
754 elf_dirty_reloc_sym(elf, old);
756 if (elf_update_symbol(elf, symtab, symtab_shndx, old)) {
757 WARN("elf_update_symbol move");
761 new_idx = first_non_local;
765 * Either way, we will add a LOCAL symbol.
767 symtab->sh.sh_info += 1;
771 if (elf_update_symbol(elf, symtab, symtab_shndx, sym)) {
772 WARN("elf_update_symbol");
776 symtab->sh.sh_size += symtab->sh.sh_entsize;
777 symtab->changed = true;
780 symtab_shndx->sh.sh_size += sizeof(Elf32_Word);
781 symtab_shndx->changed = true;
787 static struct symbol *
788 elf_create_section_symbol(struct elf *elf, struct section *sec)
790 struct symbol *sym = calloc(1, sizeof(*sym));
797 sym->name = sec->name;
801 sym->sym.st_info = GELF_ST_INFO(STB_LOCAL, STT_SECTION);
806 sym = __elf_create_symbol(elf, sym);
808 elf_add_symbol(elf, sym);
813 static int elf_add_string(struct elf *elf, struct section *strtab, char *str);
816 elf_create_prefix_symbol(struct elf *elf, struct symbol *orig, long size)
818 struct symbol *sym = calloc(1, sizeof(*sym));
819 size_t namelen = strlen(orig->name) + sizeof("__pfx_");
820 char *name = malloc(namelen);
827 snprintf(name, namelen, "__pfx_%s", orig->name);
830 sym->sec = orig->sec;
832 sym->sym.st_name = elf_add_string(elf, NULL, name);
833 sym->sym.st_info = orig->sym.st_info;
834 sym->sym.st_value = orig->sym.st_value - size;
835 sym->sym.st_size = size;
837 sym = __elf_create_symbol(elf, sym);
839 elf_add_symbol(elf, sym);
844 int elf_add_reloc_to_insn(struct elf *elf, struct section *sec,
845 unsigned long offset, unsigned int type,
846 struct section *insn_sec, unsigned long insn_off)
848 struct symbol *sym = insn_sec->sym;
849 int addend = insn_off;
853 * Due to how weak functions work, we must use section based
854 * relocations. Symbol based relocations would result in the
855 * weak and non-weak function annotations being overlaid on the
856 * non-weak function after linking.
858 sym = elf_create_section_symbol(elf, insn_sec);
865 return elf_add_reloc(elf, sec, offset, type, sym, addend);
868 static int read_rel_reloc(struct section *sec, int i, struct reloc *reloc, unsigned int *symndx)
870 if (!gelf_getrel(sec->data, i, &reloc->rel)) {
871 WARN_ELF("gelf_getrel");
874 reloc->type = GELF_R_TYPE(reloc->rel.r_info);
876 reloc->offset = reloc->rel.r_offset;
877 *symndx = GELF_R_SYM(reloc->rel.r_info);
881 static int read_rela_reloc(struct section *sec, int i, struct reloc *reloc, unsigned int *symndx)
883 if (!gelf_getrela(sec->data, i, &reloc->rela)) {
884 WARN_ELF("gelf_getrela");
887 reloc->type = GELF_R_TYPE(reloc->rela.r_info);
888 reloc->addend = reloc->rela.r_addend;
889 reloc->offset = reloc->rela.r_offset;
890 *symndx = GELF_R_SYM(reloc->rela.r_info);
894 static int read_relocs(struct elf *elf)
896 unsigned long nr_reloc, max_reloc = 0, tot_reloc = 0;
903 if (!elf_alloc_hash(reloc, elf->text_size / 16))
906 list_for_each_entry(sec, &elf->sections, list) {
907 if ((sec->sh.sh_type != SHT_RELA) &&
908 (sec->sh.sh_type != SHT_REL))
911 sec->base = find_section_by_index(elf, sec->sh.sh_info);
913 WARN("can't find base section for reloc section %s",
918 sec->base->reloc = sec;
921 for (i = 0; i < sec->sh.sh_size / sec->sh.sh_entsize; i++) {
922 reloc = malloc(sizeof(*reloc));
927 memset(reloc, 0, sizeof(*reloc));
928 switch (sec->sh.sh_type) {
930 if (read_rel_reloc(sec, i, reloc, &symndx))
934 if (read_rela_reloc(sec, i, reloc, &symndx))
942 reloc->sym = sym = find_symbol_by_index(elf, symndx);
944 WARN("can't find reloc entry symbol %d for %s",
949 list_add_tail(&reloc->sym_reloc_entry, &sym->reloc_list);
950 list_add_tail(&reloc->list, &sec->reloc_list);
951 elf_hash_add(reloc, &reloc->hash, reloc_hash(reloc));
955 max_reloc = max(max_reloc, nr_reloc);
956 tot_reloc += nr_reloc;
960 printf("max_reloc: %lu\n", max_reloc);
961 printf("tot_reloc: %lu\n", tot_reloc);
962 printf("reloc_bits: %d\n", elf->reloc_bits);
968 struct elf *elf_open_read(const char *name, int flags)
973 elf_version(EV_CURRENT);
975 elf = malloc(sizeof(*elf));
980 memset(elf, 0, offsetof(struct elf, sections));
982 INIT_LIST_HEAD(&elf->sections);
984 elf->fd = open(name, flags);
986 fprintf(stderr, "objtool: Can't open '%s': %s\n",
987 name, strerror(errno));
991 if ((flags & O_ACCMODE) == O_RDONLY)
992 cmd = ELF_C_READ_MMAP;
993 else if ((flags & O_ACCMODE) == O_RDWR)
998 elf->elf = elf_begin(elf->fd, cmd, NULL);
1000 WARN_ELF("elf_begin");
1004 if (!gelf_getehdr(elf->elf, &elf->ehdr)) {
1005 WARN_ELF("gelf_getehdr");
1009 if (read_sections(elf))
1012 if (read_symbols(elf))
1015 if (read_relocs(elf))
1025 static int elf_add_string(struct elf *elf, struct section *strtab, char *str)
1032 strtab = find_section_by_name(elf, ".strtab");
1034 WARN("can't find .strtab section");
1038 s = elf_getscn(elf->elf, strtab->idx);
1040 WARN_ELF("elf_getscn");
1044 data = elf_newdata(s);
1046 WARN_ELF("elf_newdata");
1051 data->d_size = strlen(str) + 1;
1054 len = strtab->sh.sh_size;
1055 strtab->sh.sh_size += data->d_size;
1056 strtab->changed = true;
1061 struct section *elf_create_section(struct elf *elf, const char *name,
1062 unsigned int sh_flags, size_t entsize, int nr)
1064 struct section *sec, *shstrtab;
1065 size_t size = entsize * nr;
1068 sec = malloc(sizeof(*sec));
1073 memset(sec, 0, sizeof(*sec));
1075 INIT_LIST_HEAD(&sec->symbol_list);
1076 INIT_LIST_HEAD(&sec->reloc_list);
1078 s = elf_newscn(elf->elf);
1080 WARN_ELF("elf_newscn");
1084 sec->name = strdup(name);
1090 sec->idx = elf_ndxscn(s);
1091 sec->changed = true;
1093 sec->data = elf_newdata(s);
1095 WARN_ELF("elf_newdata");
1099 sec->data->d_size = size;
1100 sec->data->d_align = 1;
1103 sec->data->d_buf = malloc(size);
1104 if (!sec->data->d_buf) {
1108 memset(sec->data->d_buf, 0, size);
1111 if (!gelf_getshdr(s, &sec->sh)) {
1112 WARN_ELF("gelf_getshdr");
1116 sec->sh.sh_size = size;
1117 sec->sh.sh_entsize = entsize;
1118 sec->sh.sh_type = SHT_PROGBITS;
1119 sec->sh.sh_addralign = 1;
1120 sec->sh.sh_flags = SHF_ALLOC | sh_flags;
1122 /* Add section name to .shstrtab (or .strtab for Clang) */
1123 shstrtab = find_section_by_name(elf, ".shstrtab");
1125 shstrtab = find_section_by_name(elf, ".strtab");
1127 WARN("can't find .shstrtab or .strtab section");
1130 sec->sh.sh_name = elf_add_string(elf, shstrtab, sec->name);
1131 if (sec->sh.sh_name == -1)
1134 list_add_tail(&sec->list, &elf->sections);
1135 elf_hash_add(section, &sec->hash, sec->idx);
1136 elf_hash_add(section_name, &sec->name_hash, str_hash(sec->name));
1138 elf->changed = true;
1143 static struct section *elf_create_rel_reloc_section(struct elf *elf, struct section *base)
1146 struct section *sec;
1148 relocname = malloc(strlen(base->name) + strlen(".rel") + 1);
1153 strcpy(relocname, ".rel");
1154 strcat(relocname, base->name);
1156 sec = elf_create_section(elf, relocname, 0, sizeof(GElf_Rel), 0);
1164 sec->sh.sh_type = SHT_REL;
1165 sec->sh.sh_addralign = 8;
1166 sec->sh.sh_link = find_section_by_name(elf, ".symtab")->idx;
1167 sec->sh.sh_info = base->idx;
1168 sec->sh.sh_flags = SHF_INFO_LINK;
1173 static struct section *elf_create_rela_reloc_section(struct elf *elf, struct section *base)
1176 struct section *sec;
1177 int addrsize = elf_class_addrsize(elf);
1179 relocname = malloc(strlen(base->name) + strlen(".rela") + 1);
1184 strcpy(relocname, ".rela");
1185 strcat(relocname, base->name);
1187 if (addrsize == sizeof(u32))
1188 sec = elf_create_section(elf, relocname, 0, sizeof(Elf32_Rela), 0);
1190 sec = elf_create_section(elf, relocname, 0, sizeof(GElf_Rela), 0);
1198 sec->sh.sh_type = SHT_RELA;
1199 sec->sh.sh_addralign = addrsize;
1200 sec->sh.sh_link = find_section_by_name(elf, ".symtab")->idx;
1201 sec->sh.sh_info = base->idx;
1202 sec->sh.sh_flags = SHF_INFO_LINK;
1207 static struct section *elf_create_reloc_section(struct elf *elf,
1208 struct section *base,
1212 case SHT_REL: return elf_create_rel_reloc_section(elf, base);
1213 case SHT_RELA: return elf_create_rela_reloc_section(elf, base);
1214 default: return NULL;
1218 static int elf_rebuild_rel_reloc_section(struct section *sec)
1220 struct reloc *reloc;
1224 /* Allocate a buffer for relocations */
1225 buf = malloc(sec->sh.sh_size);
1231 sec->data->d_buf = buf;
1232 sec->data->d_size = sec->sh.sh_size;
1233 sec->data->d_type = ELF_T_REL;
1236 list_for_each_entry(reloc, &sec->reloc_list, list) {
1237 reloc->rel.r_offset = reloc->offset;
1238 reloc->rel.r_info = GELF_R_INFO(reloc->sym->idx, reloc->type);
1239 if (!gelf_update_rel(sec->data, idx, &reloc->rel)) {
1240 WARN_ELF("gelf_update_rel");
1249 static int elf_rebuild_rela_reloc_section(struct section *sec)
1251 struct reloc *reloc;
1255 /* Allocate a buffer for relocations with addends */
1256 buf = malloc(sec->sh.sh_size);
1262 sec->data->d_buf = buf;
1263 sec->data->d_size = sec->sh.sh_size;
1264 sec->data->d_type = ELF_T_RELA;
1267 list_for_each_entry(reloc, &sec->reloc_list, list) {
1268 reloc->rela.r_offset = reloc->offset;
1269 reloc->rela.r_addend = reloc->addend;
1270 reloc->rela.r_info = GELF_R_INFO(reloc->sym->idx, reloc->type);
1271 if (!gelf_update_rela(sec->data, idx, &reloc->rela)) {
1272 WARN_ELF("gelf_update_rela");
1281 static int elf_rebuild_reloc_section(struct elf *elf, struct section *sec)
1283 switch (sec->sh.sh_type) {
1284 case SHT_REL: return elf_rebuild_rel_reloc_section(sec);
1285 case SHT_RELA: return elf_rebuild_rela_reloc_section(sec);
1290 int elf_write_insn(struct elf *elf, struct section *sec,
1291 unsigned long offset, unsigned int len,
1294 Elf_Data *data = sec->data;
1296 if (data->d_type != ELF_T_BYTE || data->d_off) {
1297 WARN("write to unexpected data for section: %s", sec->name);
1301 memcpy(data->d_buf + offset, insn, len);
1302 elf_flagdata(data, ELF_C_SET, ELF_F_DIRTY);
1304 elf->changed = true;
1309 int elf_write_reloc(struct elf *elf, struct reloc *reloc)
1311 struct section *sec = reloc->sec;
1313 if (sec->sh.sh_type == SHT_REL) {
1314 reloc->rel.r_info = GELF_R_INFO(reloc->sym->idx, reloc->type);
1315 reloc->rel.r_offset = reloc->offset;
1317 if (!gelf_update_rel(sec->data, reloc->idx, &reloc->rel)) {
1318 WARN_ELF("gelf_update_rel");
1322 reloc->rela.r_info = GELF_R_INFO(reloc->sym->idx, reloc->type);
1323 reloc->rela.r_addend = reloc->addend;
1324 reloc->rela.r_offset = reloc->offset;
1326 if (!gelf_update_rela(sec->data, reloc->idx, &reloc->rela)) {
1327 WARN_ELF("gelf_update_rela");
1332 elf->changed = true;
1338 * When Elf_Scn::sh_size is smaller than the combined Elf_Data::d_size
1341 * A) adhere to the section header and truncate the data, or
1342 * B) ignore the section header and write out all the data you've got?
1344 * Yes, libelf sucks and we need to manually truncate if we over-allocate data.
1346 static int elf_truncate_section(struct elf *elf, struct section *sec)
1348 u64 size = sec->sh.sh_size;
1349 bool truncated = false;
1350 Elf_Data *data = NULL;
1353 s = elf_getscn(elf->elf, sec->idx);
1355 WARN_ELF("elf_getscn");
1360 /* get next data descriptor for the relevant section */
1361 data = elf_getdata(s, data);
1365 WARN("end of section data but non-zero size left\n");
1372 /* when we remove symbols */
1373 WARN("truncated; but more data\n");
1377 if (!data->d_size) {
1378 WARN("zero size data");
1382 if (data->d_size > size) {
1384 data->d_size = size;
1387 size -= data->d_size;
1391 int elf_write(struct elf *elf)
1393 struct section *sec;
1399 /* Update changed relocation sections and section headers: */
1400 list_for_each_entry(sec, &elf->sections, list) {
1402 elf_truncate_section(elf, sec);
1405 s = elf_getscn(elf->elf, sec->idx);
1407 WARN_ELF("elf_getscn");
1410 if (!gelf_update_shdr(s, &sec->sh)) {
1411 WARN_ELF("gelf_update_shdr");
1416 elf_rebuild_reloc_section(elf, sec)) {
1417 WARN("elf_rebuild_reloc_section");
1421 sec->changed = false;
1422 elf->changed = true;
1426 /* Make sure the new section header entries get updated properly. */
1427 elf_flagelf(elf->elf, ELF_C_SET, ELF_F_DIRTY);
1429 /* Write all changes to the file. */
1430 if (elf_update(elf->elf, ELF_C_WRITE) < 0) {
1431 WARN_ELF("elf_update");
1435 elf->changed = false;
1440 void elf_close(struct elf *elf)
1442 struct section *sec, *tmpsec;
1443 struct symbol *sym, *tmpsym;
1444 struct reloc *reloc, *tmpreloc;
1452 list_for_each_entry_safe(sec, tmpsec, &elf->sections, list) {
1453 list_for_each_entry_safe(sym, tmpsym, &sec->symbol_list, list) {
1454 list_del(&sym->list);
1455 hash_del(&sym->hash);
1458 list_for_each_entry_safe(reloc, tmpreloc, &sec->reloc_list, list) {
1459 list_del(&reloc->list);
1460 hash_del(&reloc->hash);
1463 list_del(&sec->list);