| // SPDX-License-Identifier: GPL-2.0-or-later |
| /* |
| * elf.c - ELF access library |
| * |
| * Adapted from kpatch (https://github.com/dynup/kpatch): |
| * Copyright (C) 2013-2015 Josh Poimboeuf <jpoimboe@redhat.com> |
| * Copyright (C) 2014 Seth Jennings <sjenning@redhat.com> |
| */ |
| |
| #include <sys/types.h> |
| #include <sys/stat.h> |
| #include <fcntl.h> |
| #include <stdio.h> |
| #include <stdlib.h> |
| #include <string.h> |
| #include <unistd.h> |
| #include <errno.h> |
| |
| #include "elf.h" |
| #include "warn.h" |
| |
| #define MAX_NAME_LEN 128 |
| |
| struct section *find_section_by_name(struct elf *elf, const char *name) |
| { |
| struct section *sec; |
| |
| list_for_each_entry(sec, &elf->sections, list) |
| if (!strcmp(sec->name, name)) |
| return sec; |
| |
| return NULL; |
| } |
| |
| static struct section *find_section_by_index(struct elf *elf, |
| unsigned int idx) |
| { |
| struct section *sec; |
| |
| list_for_each_entry(sec, &elf->sections, list) |
| if (sec->idx == idx) |
| return sec; |
| |
| return NULL; |
| } |
| |
| static struct symbol *find_symbol_by_index(struct elf *elf, unsigned int idx) |
| { |
| struct section *sec; |
| struct symbol *sym; |
| |
| list_for_each_entry(sec, &elf->sections, list) |
| hash_for_each_possible(sec->symbol_hash, sym, hash, idx) |
| if (sym->idx == idx) |
| return sym; |
| |
| return NULL; |
| } |
| |
| struct symbol *find_symbol_by_offset(struct section *sec, unsigned long offset) |
| { |
| struct symbol *sym; |
| |
| list_for_each_entry(sym, &sec->symbol_list, list) |
| if (sym->type != STT_SECTION && |
| sym->offset == offset) |
| return sym; |
| |
| return NULL; |
| } |
| |
| struct symbol *find_symbol_by_name(struct elf *elf, const char *name) |
| { |
| struct section *sec; |
| struct symbol *sym; |
| |
| list_for_each_entry(sec, &elf->sections, list) |
| list_for_each_entry(sym, &sec->symbol_list, list) |
| if (!strcmp(sym->name, name)) |
| return sym; |
| |
| return NULL; |
| } |
| |
| struct symbol *find_symbol_containing(struct section *sec, unsigned long offset) |
| { |
| struct symbol *sym; |
| |
| list_for_each_entry(sym, &sec->symbol_list, list) |
| if (sym->type != STT_SECTION && |
| offset >= sym->offset && offset < sym->offset + sym->len) |
| return sym; |
| |
| return NULL; |
| } |
| |
| struct rela *find_rela_by_dest_range(struct section *sec, unsigned long offset, |
| unsigned int len) |
| { |
| struct rela *rela; |
| unsigned long o; |
| |
| if (!sec->rela) |
| return NULL; |
| |
| for (o = offset; o < offset + len; o++) |
| hash_for_each_possible(sec->rela->rela_hash, rela, hash, o) |
| if (rela->offset == o) |
| return rela; |
| |
| return NULL; |
| } |
| |
| struct rela *find_rela_by_dest(struct section *sec, unsigned long offset) |
| { |
| return find_rela_by_dest_range(sec, offset, 1); |
| } |
| |
| struct symbol *find_containing_func(struct section *sec, unsigned long offset) |
| { |
| struct symbol *func; |
| |
| list_for_each_entry(func, &sec->symbol_list, list) |
| if (func->type == STT_FUNC && offset >= func->offset && |
| offset < func->offset + func->len) |
| return func; |
| |
| return NULL; |
| } |
| |
| static int read_sections(struct elf *elf) |
| { |
| Elf_Scn *s = NULL; |
| struct section *sec; |
| size_t shstrndx, sections_nr; |
| int i; |
| |
| if (elf_getshdrnum(elf->elf, §ions_nr)) { |
| WARN_ELF("elf_getshdrnum"); |
| return -1; |
| } |
| |
| if (elf_getshdrstrndx(elf->elf, &shstrndx)) { |
| WARN_ELF("elf_getshdrstrndx"); |
| return -1; |
| } |
| |
| for (i = 0; i < sections_nr; i++) { |
| sec = malloc(sizeof(*sec)); |
| if (!sec) { |
| perror("malloc"); |
| return -1; |
| } |
| memset(sec, 0, sizeof(*sec)); |
| |
| INIT_LIST_HEAD(&sec->symbol_list); |
| INIT_LIST_HEAD(&sec->rela_list); |
| hash_init(sec->rela_hash); |
| hash_init(sec->symbol_hash); |
| |
| list_add_tail(&sec->list, &elf->sections); |
| |
| s = elf_getscn(elf->elf, i); |
| if (!s) { |
| WARN_ELF("elf_getscn"); |
| return -1; |
| } |
| |
| sec->idx = elf_ndxscn(s); |
| |
| if (!gelf_getshdr(s, &sec->sh)) { |
| WARN_ELF("gelf_getshdr"); |
| return -1; |
| } |
| |
| sec->name = elf_strptr(elf->elf, shstrndx, sec->sh.sh_name); |
| if (!sec->name) { |
| WARN_ELF("elf_strptr"); |
| return -1; |
| } |
| |
| if (sec->sh.sh_size != 0) { |
| sec->data = elf_getdata(s, NULL); |
| if (!sec->data) { |
| WARN_ELF("elf_getdata"); |
| return -1; |
| } |
| if (sec->data->d_off != 0 || |
| sec->data->d_size != sec->sh.sh_size) { |
| WARN("unexpected data attributes for %s", |
| sec->name); |
| return -1; |
| } |
| } |
| sec->len = sec->sh.sh_size; |
| } |
| |
| /* sanity check, one more call to elf_nextscn() should return NULL */ |
| if (elf_nextscn(elf->elf, s)) { |
| WARN("section entry mismatch"); |
| return -1; |
| } |
| |
| return 0; |
| } |
| |
| static int read_symbols(struct elf *elf) |
| { |
| struct section *symtab, *sec; |
| struct symbol *sym, *pfunc, *alias; |
| struct list_head *entry, *tmp; |
| int symbols_nr, i; |
| char *coldstr; |
| |
| symtab = find_section_by_name(elf, ".symtab"); |
| if (!symtab) { |
| /* |
| * A missing symbol table is actually possible if it's an empty |
| * .o file. This can happen for thunk_64.o. |
| */ |
| return 0; |
| } |
| |
| symbols_nr = symtab->sh.sh_size / symtab->sh.sh_entsize; |
| |
| for (i = 0; i < symbols_nr; i++) { |
| sym = malloc(sizeof(*sym)); |
| if (!sym) { |
| perror("malloc"); |
| return -1; |
| } |
| memset(sym, 0, sizeof(*sym)); |
| alias = sym; |
| |
| sym->idx = i; |
| |
| if (!gelf_getsym(symtab->data, i, &sym->sym)) { |
| WARN_ELF("gelf_getsym"); |
| goto err; |
| } |
| |
| sym->name = elf_strptr(elf->elf, symtab->sh.sh_link, |
| sym->sym.st_name); |
| if (!sym->name) { |
| WARN_ELF("elf_strptr"); |
| goto err; |
| } |
| |
| sym->type = GELF_ST_TYPE(sym->sym.st_info); |
| sym->bind = GELF_ST_BIND(sym->sym.st_info); |
| |
| if (sym->sym.st_shndx > SHN_UNDEF && |
| sym->sym.st_shndx < SHN_LORESERVE) { |
| sym->sec = find_section_by_index(elf, |
| sym->sym.st_shndx); |
| if (!sym->sec) { |
| WARN("couldn't find section for symbol %s", |
| sym->name); |
| goto err; |
| } |
| if (sym->type == STT_SECTION) { |
| sym->name = sym->sec->name; |
| sym->sec->sym = sym; |
| } |
| } else |
| sym->sec = find_section_by_index(elf, 0); |
| |
| sym->offset = sym->sym.st_value; |
| sym->len = sym->sym.st_size; |
| |
| /* sorted insert into a per-section list */ |
| entry = &sym->sec->symbol_list; |
| list_for_each_prev(tmp, &sym->sec->symbol_list) { |
| struct symbol *s; |
| |
| s = list_entry(tmp, struct symbol, list); |
| |
| if (sym->offset > s->offset) { |
| entry = tmp; |
| break; |
| } |
| |
| if (sym->offset == s->offset) { |
| if (sym->len && sym->len == s->len && alias == sym) |
| alias = s; |
| |
| if (sym->len >= s->len) { |
| entry = tmp; |
| break; |
| } |
| } |
| } |
| sym->alias = alias; |
| list_add(&sym->list, entry); |
| hash_add(sym->sec->symbol_hash, &sym->hash, sym->idx); |
| } |
| |
| /* Create parent/child links for any cold subfunctions */ |
| list_for_each_entry(sec, &elf->sections, list) { |
| list_for_each_entry(sym, &sec->symbol_list, list) { |
| char pname[MAX_NAME_LEN + 1]; |
| size_t pnamelen; |
| if (sym->type != STT_FUNC) |
| continue; |
| sym->pfunc = sym->cfunc = sym; |
| coldstr = strstr(sym->name, ".cold"); |
| if (!coldstr) |
| continue; |
| |
| pnamelen = coldstr - sym->name; |
| if (pnamelen > MAX_NAME_LEN) { |
| WARN("%s(): parent function name exceeds maximum length of %d characters", |
| sym->name, MAX_NAME_LEN); |
| return -1; |
| } |
| |
| strncpy(pname, sym->name, pnamelen); |
| pname[pnamelen] = '\0'; |
| pfunc = find_symbol_by_name(elf, pname); |
| |
| if (!pfunc) { |
| WARN("%s(): can't find parent function", |
| sym->name); |
| return -1; |
| } |
| |
| sym->pfunc = pfunc; |
| pfunc->cfunc = sym; |
| |
| /* |
| * Unfortunately, -fnoreorder-functions puts the child |
| * inside the parent. Remove the overlap so we can |
| * have sane assumptions. |
| * |
| * Note that pfunc->len now no longer matches |
| * pfunc->sym.st_size. |
| */ |
| if (sym->sec == pfunc->sec && |
| sym->offset >= pfunc->offset && |
| sym->offset + sym->len == pfunc->offset + pfunc->len) { |
| pfunc->len -= sym->len; |
| } |
| } |
| } |
| |
| return 0; |
| |
| err: |
| free(sym); |
| return -1; |
| } |
| |
| static int read_relas(struct elf *elf) |
| { |
| struct section *sec; |
| struct rela *rela; |
| int i; |
| unsigned int symndx; |
| |
| list_for_each_entry(sec, &elf->sections, list) { |
| if (sec->sh.sh_type != SHT_RELA) |
| continue; |
| |
| sec->base = find_section_by_name(elf, sec->name + 5); |
| if (!sec->base) { |
| WARN("can't find base section for rela section %s", |
| sec->name); |
| return -1; |
| } |
| |
| sec->base->rela = sec; |
| |
| for (i = 0; i < sec->sh.sh_size / sec->sh.sh_entsize; i++) { |
| rela = malloc(sizeof(*rela)); |
| if (!rela) { |
| perror("malloc"); |
| return -1; |
| } |
| memset(rela, 0, sizeof(*rela)); |
| |
| if (!gelf_getrela(sec->data, i, &rela->rela)) { |
| WARN_ELF("gelf_getrela"); |
| return -1; |
| } |
| |
| rela->type = GELF_R_TYPE(rela->rela.r_info); |
| rela->addend = rela->rela.r_addend; |
| rela->offset = rela->rela.r_offset; |
| symndx = GELF_R_SYM(rela->rela.r_info); |
| rela->sym = find_symbol_by_index(elf, symndx); |
| rela->sec = sec; |
| if (!rela->sym) { |
| WARN("can't find rela entry symbol %d for %s", |
| symndx, sec->name); |
| return -1; |
| } |
| |
| list_add_tail(&rela->list, &sec->rela_list); |
| hash_add(sec->rela_hash, &rela->hash, rela->offset); |
| |
| } |
| } |
| |
| return 0; |
| } |
| |
| struct elf *elf_read(const char *name, int flags) |
| { |
| struct elf *elf; |
| Elf_Cmd cmd; |
| |
| elf_version(EV_CURRENT); |
| |
| elf = malloc(sizeof(*elf)); |
| if (!elf) { |
| perror("malloc"); |
| return NULL; |
| } |
| memset(elf, 0, sizeof(*elf)); |
| |
| INIT_LIST_HEAD(&elf->sections); |
| |
| elf->fd = open(name, flags); |
| if (elf->fd == -1) { |
| fprintf(stderr, "objtool: Can't open '%s': %s\n", |
| name, strerror(errno)); |
| goto err; |
| } |
| |
| if ((flags & O_ACCMODE) == O_RDONLY) |
| cmd = ELF_C_READ_MMAP; |
| else if ((flags & O_ACCMODE) == O_RDWR) |
| cmd = ELF_C_RDWR; |
| else /* O_WRONLY */ |
| cmd = ELF_C_WRITE; |
| |
| elf->elf = elf_begin(elf->fd, cmd, NULL); |
| if (!elf->elf) { |
| WARN_ELF("elf_begin"); |
| goto err; |
| } |
| |
| if (!gelf_getehdr(elf->elf, &elf->ehdr)) { |
| WARN_ELF("gelf_getehdr"); |
| goto err; |
| } |
| |
| if (read_sections(elf)) |
| goto err; |
| |
| if (read_symbols(elf)) |
| goto err; |
| |
| if (read_relas(elf)) |
| goto err; |
| |
| return elf; |
| |
| err: |
| elf_close(elf); |
| return NULL; |
| } |
| |
| struct section *elf_create_section(struct elf *elf, const char *name, |
| size_t entsize, int nr) |
| { |
| struct section *sec, *shstrtab; |
| size_t size = entsize * nr; |
| Elf_Scn *s; |
| Elf_Data *data; |
| |
| sec = malloc(sizeof(*sec)); |
| if (!sec) { |
| perror("malloc"); |
| return NULL; |
| } |
| memset(sec, 0, sizeof(*sec)); |
| |
| INIT_LIST_HEAD(&sec->symbol_list); |
| INIT_LIST_HEAD(&sec->rela_list); |
| hash_init(sec->rela_hash); |
| hash_init(sec->symbol_hash); |
| |
| list_add_tail(&sec->list, &elf->sections); |
| |
| s = elf_newscn(elf->elf); |
| if (!s) { |
| WARN_ELF("elf_newscn"); |
| return NULL; |
| } |
| |
| sec->name = strdup(name); |
| if (!sec->name) { |
| perror("strdup"); |
| return NULL; |
| } |
| |
| sec->idx = elf_ndxscn(s); |
| sec->len = size; |
| sec->changed = true; |
| |
| sec->data = elf_newdata(s); |
| if (!sec->data) { |
| WARN_ELF("elf_newdata"); |
| return NULL; |
| } |
| |
| sec->data->d_size = size; |
| sec->data->d_align = 1; |
| |
| if (size) { |
| sec->data->d_buf = malloc(size); |
| if (!sec->data->d_buf) { |
| perror("malloc"); |
| return NULL; |
| } |
| memset(sec->data->d_buf, 0, size); |
| } |
| |
| if (!gelf_getshdr(s, &sec->sh)) { |
| WARN_ELF("gelf_getshdr"); |
| return NULL; |
| } |
| |
| sec->sh.sh_size = size; |
| sec->sh.sh_entsize = entsize; |
| sec->sh.sh_type = SHT_PROGBITS; |
| sec->sh.sh_addralign = 1; |
| sec->sh.sh_flags = SHF_ALLOC; |
| |
| |
| /* Add section name to .shstrtab (or .strtab for Clang) */ |
| shstrtab = find_section_by_name(elf, ".shstrtab"); |
| if (!shstrtab) |
| shstrtab = find_section_by_name(elf, ".strtab"); |
| if (!shstrtab) { |
| WARN("can't find .shstrtab or .strtab section"); |
| return NULL; |
| } |
| |
| s = elf_getscn(elf->elf, shstrtab->idx); |
| if (!s) { |
| WARN_ELF("elf_getscn"); |
| return NULL; |
| } |
| |
| data = elf_newdata(s); |
| if (!data) { |
| WARN_ELF("elf_newdata"); |
| return NULL; |
| } |
| |
| data->d_buf = sec->name; |
| data->d_size = strlen(name) + 1; |
| data->d_align = 1; |
| |
| sec->sh.sh_name = shstrtab->len; |
| |
| shstrtab->len += strlen(name) + 1; |
| shstrtab->changed = true; |
| |
| return sec; |
| } |
| |
| struct section *elf_create_rela_section(struct elf *elf, struct section *base) |
| { |
| char *relaname; |
| struct section *sec; |
| |
| relaname = malloc(strlen(base->name) + strlen(".rela") + 1); |
| if (!relaname) { |
| perror("malloc"); |
| return NULL; |
| } |
| strcpy(relaname, ".rela"); |
| strcat(relaname, base->name); |
| |
| sec = elf_create_section(elf, relaname, sizeof(GElf_Rela), 0); |
| free(relaname); |
| if (!sec) |
| return NULL; |
| |
| base->rela = sec; |
| sec->base = base; |
| |
| sec->sh.sh_type = SHT_RELA; |
| sec->sh.sh_addralign = 8; |
| sec->sh.sh_link = find_section_by_name(elf, ".symtab")->idx; |
| sec->sh.sh_info = base->idx; |
| sec->sh.sh_flags = SHF_INFO_LINK; |
| |
| return sec; |
| } |
| |
| int elf_rebuild_rela_section(struct section *sec) |
| { |
| struct rela *rela; |
| int nr, idx = 0, size; |
| GElf_Rela *relas; |
| |
| nr = 0; |
| list_for_each_entry(rela, &sec->rela_list, list) |
| nr++; |
| |
| size = nr * sizeof(*relas); |
| relas = malloc(size); |
| if (!relas) { |
| perror("malloc"); |
| return -1; |
| } |
| |
| sec->data->d_buf = relas; |
| sec->data->d_size = size; |
| |
| sec->sh.sh_size = size; |
| |
| idx = 0; |
| list_for_each_entry(rela, &sec->rela_list, list) { |
| relas[idx].r_offset = rela->offset; |
| relas[idx].r_addend = rela->addend; |
| relas[idx].r_info = GELF_R_INFO(rela->sym->idx, rela->type); |
| idx++; |
| } |
| |
| return 0; |
| } |
| |
| int elf_write(struct elf *elf) |
| { |
| struct section *sec; |
| Elf_Scn *s; |
| |
| /* Update section headers for changed sections: */ |
| list_for_each_entry(sec, &elf->sections, list) { |
| if (sec->changed) { |
| s = elf_getscn(elf->elf, sec->idx); |
| if (!s) { |
| WARN_ELF("elf_getscn"); |
| return -1; |
| } |
| if (!gelf_update_shdr(s, &sec->sh)) { |
| WARN_ELF("gelf_update_shdr"); |
| return -1; |
| } |
| } |
| } |
| |
| /* Make sure the new section header entries get updated properly. */ |
| elf_flagelf(elf->elf, ELF_C_SET, ELF_F_DIRTY); |
| |
| /* Write all changes to the file. */ |
| if (elf_update(elf->elf, ELF_C_WRITE) < 0) { |
| WARN_ELF("elf_update"); |
| return -1; |
| } |
| |
| return 0; |
| } |
| |
| void elf_close(struct elf *elf) |
| { |
| struct section *sec, *tmpsec; |
| struct symbol *sym, *tmpsym; |
| struct rela *rela, *tmprela; |
| |
| if (elf->elf) |
| elf_end(elf->elf); |
| |
| if (elf->fd > 0) |
| close(elf->fd); |
| |
| list_for_each_entry_safe(sec, tmpsec, &elf->sections, list) { |
| list_for_each_entry_safe(sym, tmpsym, &sec->symbol_list, list) { |
| list_del(&sym->list); |
| hash_del(&sym->hash); |
| free(sym); |
| } |
| list_for_each_entry_safe(rela, tmprela, &sec->rela_list, list) { |
| list_del(&rela->list); |
| hash_del(&rela->hash); |
| free(rela); |
| } |
| list_del(&sec->list); |
| free(sec); |
| } |
| |
| free(elf); |
| } |