| /* |
| * 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> |
| * |
| * This program is free software; you can redistribute it and/or |
| * modify it under the terms of the GNU General Public License |
| * as published by the Free Software Foundation; either version 2 |
| * of the License, or (at your option) any later version. |
| * |
| * This program is distributed in the hope that it will be useful, |
| * but WITHOUT ANY WARRANTY; without even the implied warranty of |
| * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
| * GNU General Public License for more details. |
| * |
| * You should have received a copy of the GNU General Public License |
| * along with this program; if not, see <http://www.gnu.org/licenses/>. |
| */ |
| |
| #include <sys/types.h> |
| #include <sys/stat.h> |
| #include <fcntl.h> |
| #include <stdio.h> |
| #include <stdlib.h> |
| #include <string.h> |
| #include <unistd.h> |
| |
| #include "elf.h" |
| #include "warn.h" |
| |
| 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) |
| list_for_each_entry(sym, &sec->symbols, list) |
| 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->symbols, list) |
| if (sym->type != STT_SECTION && |
| sym->offset == offset) |
| return sym; |
| |
| return NULL; |
| } |
| |
| struct rela *find_rela_by_dest_range(struct section *sec, unsigned long offset, |
| unsigned int len) |
| { |
| struct rela *rela; |
| |
| if (!sec->rela) |
| return NULL; |
| |
| list_for_each_entry(rela, &sec->rela->relas, list) |
| if (rela->offset >= offset && rela->offset < offset + len) |
| 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->symbols, 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)) { |
| perror("elf_getshdrnum"); |
| return -1; |
| } |
| |
| if (elf_getshdrstrndx(elf->elf, &shstrndx)) { |
| perror("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->symbols); |
| INIT_LIST_HEAD(&sec->relas); |
| |
| list_add_tail(&sec->list, &elf->sections); |
| |
| s = elf_getscn(elf->elf, i); |
| if (!s) { |
| perror("elf_getscn"); |
| return -1; |
| } |
| |
| sec->idx = elf_ndxscn(s); |
| |
| if (!gelf_getshdr(s, &sec->sh)) { |
| perror("gelf_getshdr"); |
| return -1; |
| } |
| |
| sec->name = elf_strptr(elf->elf, shstrndx, sec->sh.sh_name); |
| if (!sec->name) { |
| perror("elf_strptr"); |
| return -1; |
| } |
| |
| sec->elf_data = elf_getdata(s, NULL); |
| if (!sec->elf_data) { |
| perror("elf_getdata"); |
| return -1; |
| } |
| |
| if (sec->elf_data->d_off != 0 || |
| sec->elf_data->d_size != sec->sh.sh_size) { |
| WARN("unexpected data attributes for %s", sec->name); |
| return -1; |
| } |
| |
| sec->data = (unsigned long)sec->elf_data->d_buf; |
| sec->len = sec->elf_data->d_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; |
| struct symbol *sym; |
| struct list_head *entry, *tmp; |
| int symbols_nr, i; |
| |
| symtab = find_section_by_name(elf, ".symtab"); |
| if (!symtab) { |
| WARN("missing symbol table"); |
| return -1; |
| } |
| |
| 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)); |
| |
| sym->idx = i; |
| |
| if (!gelf_getsym(symtab->elf_data, i, &sym->sym)) { |
| perror("gelf_getsym"); |
| goto err; |
| } |
| |
| sym->name = elf_strptr(elf->elf, symtab->sh.sh_link, |
| sym->sym.st_name); |
| if (!sym->name) { |
| perror("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->symbols; |
| list_for_each_prev(tmp, &sym->sec->symbols) { |
| struct symbol *s; |
| |
| s = list_entry(tmp, struct symbol, list); |
| |
| if (sym->offset > s->offset) { |
| entry = tmp; |
| break; |
| } |
| |
| if (sym->offset == s->offset && sym->len >= s->len) { |
| entry = tmp; |
| break; |
| } |
| } |
| list_add(&sym->list, entry); |
| } |
| |
| 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)); |
| |
| list_add_tail(&rela->list, &sec->relas); |
| |
| if (!gelf_getrela(sec->elf_data, i, &rela->rela)) { |
| perror("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); |
| if (!rela->sym) { |
| WARN("can't find rela entry symbol %d for %s", |
| symndx, sec->name); |
| return -1; |
| } |
| } |
| } |
| |
| return 0; |
| } |
| |
| struct elf *elf_open(const char *name) |
| { |
| struct elf *elf; |
| |
| 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->name = strdup(name); |
| if (!elf->name) { |
| perror("strdup"); |
| goto err; |
| } |
| |
| elf->fd = open(name, O_RDONLY); |
| if (elf->fd == -1) { |
| perror("open"); |
| goto err; |
| } |
| |
| elf->elf = elf_begin(elf->fd, ELF_C_READ_MMAP, NULL); |
| if (!elf->elf) { |
| perror("elf_begin"); |
| goto err; |
| } |
| |
| if (!gelf_getehdr(elf->elf, &elf->ehdr)) { |
| perror("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; |
| } |
| |
| void elf_close(struct elf *elf) |
| { |
| struct section *sec, *tmpsec; |
| struct symbol *sym, *tmpsym; |
| struct rela *rela, *tmprela; |
| |
| list_for_each_entry_safe(sec, tmpsec, &elf->sections, list) { |
| list_for_each_entry_safe(sym, tmpsym, &sec->symbols, list) { |
| list_del(&sym->list); |
| free(sym); |
| } |
| list_for_each_entry_safe(rela, tmprela, &sec->relas, list) { |
| list_del(&rela->list); |
| free(rela); |
| } |
| list_del(&sec->list); |
| free(sec); |
| } |
| if (elf->name) |
| free(elf->name); |
| if (elf->fd > 0) |
| close(elf->fd); |
| if (elf->elf) |
| elf_end(elf->elf); |
| free(elf); |
| } |