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![Arnaldo Carvalho de Melo](/assets/img/avatar_default.png)
Not all libelf implementations have this "Please, ELF_C_READ, but use mmap if possible" elf_begin() cmd, so provide a fallback to plain old ELF_C_READ. Case in point: Alpine Linux 3.4. Cc: Adrian Hunter <adrian.hunter@intel.com> Cc: David Ahern <dsahern@gmail.com> Cc: Jiri Olsa <jolsa@kernel.org> Cc: Josh Poimboeuf <jpoimboe@redhat.com> Cc: Namhyung Kim <namhyung@kernel.org> Cc: Wang Nan <wangnan0@huawei.com> Link: http://lkml.kernel.org/n/tip-1fctuknrawgoi5xqon4mu9dv@git.kernel.org Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
419 lines
8.6 KiB
C
419 lines
8.6 KiB
C
/*
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* elf.c - ELF access library
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*
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* Adapted from kpatch (https://github.com/dynup/kpatch):
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* Copyright (C) 2013-2015 Josh Poimboeuf <jpoimboe@redhat.com>
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* Copyright (C) 2014 Seth Jennings <sjenning@redhat.com>
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation; either version 2
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* of the License, or (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, see <http://www.gnu.org/licenses/>.
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*/
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#include <sys/types.h>
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#include <sys/stat.h>
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#include <fcntl.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <unistd.h>
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#include "elf.h"
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#include "warn.h"
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/*
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* Fallback for systems without this "read, mmaping if possible" cmd.
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*/
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#ifndef ELF_C_READ_MMAP
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#define ELF_C_READ_MMAP ELF_C_READ
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#endif
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struct section *find_section_by_name(struct elf *elf, const char *name)
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{
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struct section *sec;
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list_for_each_entry(sec, &elf->sections, list)
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if (!strcmp(sec->name, name))
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return sec;
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return NULL;
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}
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static struct section *find_section_by_index(struct elf *elf,
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unsigned int idx)
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{
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struct section *sec;
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list_for_each_entry(sec, &elf->sections, list)
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if (sec->idx == idx)
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return sec;
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return NULL;
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}
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static struct symbol *find_symbol_by_index(struct elf *elf, unsigned int idx)
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{
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struct section *sec;
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struct symbol *sym;
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list_for_each_entry(sec, &elf->sections, list)
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hash_for_each_possible(sec->symbol_hash, sym, hash, idx)
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if (sym->idx == idx)
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return sym;
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return NULL;
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}
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struct symbol *find_symbol_by_offset(struct section *sec, unsigned long offset)
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{
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struct symbol *sym;
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list_for_each_entry(sym, &sec->symbol_list, list)
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if (sym->type != STT_SECTION &&
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sym->offset == offset)
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return sym;
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return NULL;
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}
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struct rela *find_rela_by_dest_range(struct section *sec, unsigned long offset,
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unsigned int len)
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{
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struct rela *rela;
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unsigned long o;
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if (!sec->rela)
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return NULL;
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for (o = offset; o < offset + len; o++)
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hash_for_each_possible(sec->rela->rela_hash, rela, hash, o)
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if (rela->offset == o)
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return rela;
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return NULL;
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}
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struct rela *find_rela_by_dest(struct section *sec, unsigned long offset)
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{
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return find_rela_by_dest_range(sec, offset, 1);
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}
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struct symbol *find_containing_func(struct section *sec, unsigned long offset)
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{
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struct symbol *func;
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list_for_each_entry(func, &sec->symbol_list, list)
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if (func->type == STT_FUNC && offset >= func->offset &&
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offset < func->offset + func->len)
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return func;
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return NULL;
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}
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static int read_sections(struct elf *elf)
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{
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Elf_Scn *s = NULL;
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struct section *sec;
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size_t shstrndx, sections_nr;
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int i;
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if (elf_getshdrnum(elf->elf, §ions_nr)) {
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perror("elf_getshdrnum");
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return -1;
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}
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if (elf_getshdrstrndx(elf->elf, &shstrndx)) {
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perror("elf_getshdrstrndx");
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return -1;
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}
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for (i = 0; i < sections_nr; i++) {
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sec = malloc(sizeof(*sec));
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if (!sec) {
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perror("malloc");
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return -1;
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}
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memset(sec, 0, sizeof(*sec));
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INIT_LIST_HEAD(&sec->symbol_list);
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INIT_LIST_HEAD(&sec->rela_list);
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hash_init(sec->rela_hash);
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hash_init(sec->symbol_hash);
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list_add_tail(&sec->list, &elf->sections);
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s = elf_getscn(elf->elf, i);
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if (!s) {
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perror("elf_getscn");
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return -1;
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}
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sec->idx = elf_ndxscn(s);
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if (!gelf_getshdr(s, &sec->sh)) {
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perror("gelf_getshdr");
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return -1;
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}
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sec->name = elf_strptr(elf->elf, shstrndx, sec->sh.sh_name);
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if (!sec->name) {
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perror("elf_strptr");
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return -1;
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}
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sec->elf_data = elf_getdata(s, NULL);
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if (!sec->elf_data) {
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perror("elf_getdata");
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return -1;
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}
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if (sec->elf_data->d_off != 0 ||
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sec->elf_data->d_size != sec->sh.sh_size) {
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WARN("unexpected data attributes for %s", sec->name);
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return -1;
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}
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sec->data = (unsigned long)sec->elf_data->d_buf;
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sec->len = sec->elf_data->d_size;
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}
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/* sanity check, one more call to elf_nextscn() should return NULL */
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if (elf_nextscn(elf->elf, s)) {
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WARN("section entry mismatch");
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return -1;
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}
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return 0;
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}
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static int read_symbols(struct elf *elf)
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{
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struct section *symtab;
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struct symbol *sym;
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struct list_head *entry, *tmp;
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int symbols_nr, i;
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symtab = find_section_by_name(elf, ".symtab");
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if (!symtab) {
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WARN("missing symbol table");
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return -1;
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}
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symbols_nr = symtab->sh.sh_size / symtab->sh.sh_entsize;
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for (i = 0; i < symbols_nr; i++) {
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sym = malloc(sizeof(*sym));
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if (!sym) {
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perror("malloc");
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return -1;
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}
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memset(sym, 0, sizeof(*sym));
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sym->idx = i;
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if (!gelf_getsym(symtab->elf_data, i, &sym->sym)) {
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perror("gelf_getsym");
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goto err;
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}
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sym->name = elf_strptr(elf->elf, symtab->sh.sh_link,
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sym->sym.st_name);
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if (!sym->name) {
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perror("elf_strptr");
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goto err;
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}
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sym->type = GELF_ST_TYPE(sym->sym.st_info);
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sym->bind = GELF_ST_BIND(sym->sym.st_info);
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if (sym->sym.st_shndx > SHN_UNDEF &&
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sym->sym.st_shndx < SHN_LORESERVE) {
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sym->sec = find_section_by_index(elf,
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sym->sym.st_shndx);
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if (!sym->sec) {
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WARN("couldn't find section for symbol %s",
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sym->name);
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goto err;
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}
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if (sym->type == STT_SECTION) {
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sym->name = sym->sec->name;
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sym->sec->sym = sym;
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}
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} else
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sym->sec = find_section_by_index(elf, 0);
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sym->offset = sym->sym.st_value;
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sym->len = sym->sym.st_size;
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/* sorted insert into a per-section list */
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entry = &sym->sec->symbol_list;
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list_for_each_prev(tmp, &sym->sec->symbol_list) {
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struct symbol *s;
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s = list_entry(tmp, struct symbol, list);
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if (sym->offset > s->offset) {
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entry = tmp;
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break;
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}
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if (sym->offset == s->offset && sym->len >= s->len) {
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entry = tmp;
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break;
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}
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}
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list_add(&sym->list, entry);
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hash_add(sym->sec->symbol_hash, &sym->hash, sym->idx);
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}
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return 0;
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err:
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free(sym);
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return -1;
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}
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static int read_relas(struct elf *elf)
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{
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struct section *sec;
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struct rela *rela;
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int i;
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unsigned int symndx;
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list_for_each_entry(sec, &elf->sections, list) {
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if (sec->sh.sh_type != SHT_RELA)
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continue;
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sec->base = find_section_by_name(elf, sec->name + 5);
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if (!sec->base) {
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WARN("can't find base section for rela section %s",
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sec->name);
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return -1;
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}
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sec->base->rela = sec;
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for (i = 0; i < sec->sh.sh_size / sec->sh.sh_entsize; i++) {
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rela = malloc(sizeof(*rela));
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if (!rela) {
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perror("malloc");
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return -1;
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}
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memset(rela, 0, sizeof(*rela));
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if (!gelf_getrela(sec->elf_data, i, &rela->rela)) {
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perror("gelf_getrela");
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return -1;
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}
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rela->type = GELF_R_TYPE(rela->rela.r_info);
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rela->addend = rela->rela.r_addend;
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rela->offset = rela->rela.r_offset;
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symndx = GELF_R_SYM(rela->rela.r_info);
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rela->sym = find_symbol_by_index(elf, symndx);
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if (!rela->sym) {
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WARN("can't find rela entry symbol %d for %s",
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symndx, sec->name);
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return -1;
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}
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list_add_tail(&rela->list, &sec->rela_list);
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hash_add(sec->rela_hash, &rela->hash, rela->offset);
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}
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}
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return 0;
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}
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struct elf *elf_open(const char *name)
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{
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struct elf *elf;
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elf_version(EV_CURRENT);
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elf = malloc(sizeof(*elf));
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if (!elf) {
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perror("malloc");
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return NULL;
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}
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memset(elf, 0, sizeof(*elf));
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INIT_LIST_HEAD(&elf->sections);
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elf->name = strdup(name);
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if (!elf->name) {
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perror("strdup");
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goto err;
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}
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elf->fd = open(name, O_RDONLY);
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if (elf->fd == -1) {
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perror("open");
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goto err;
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}
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elf->elf = elf_begin(elf->fd, ELF_C_READ_MMAP, NULL);
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if (!elf->elf) {
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perror("elf_begin");
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goto err;
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}
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if (!gelf_getehdr(elf->elf, &elf->ehdr)) {
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perror("gelf_getehdr");
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goto err;
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}
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if (read_sections(elf))
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goto err;
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if (read_symbols(elf))
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goto err;
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if (read_relas(elf))
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goto err;
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return elf;
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err:
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elf_close(elf);
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return NULL;
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}
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void elf_close(struct elf *elf)
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{
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struct section *sec, *tmpsec;
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struct symbol *sym, *tmpsym;
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struct rela *rela, *tmprela;
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list_for_each_entry_safe(sec, tmpsec, &elf->sections, list) {
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list_for_each_entry_safe(sym, tmpsym, &sec->symbol_list, list) {
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list_del(&sym->list);
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hash_del(&sym->hash);
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free(sym);
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}
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list_for_each_entry_safe(rela, tmprela, &sec->rela_list, list) {
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list_del(&rela->list);
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hash_del(&rela->hash);
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free(rela);
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}
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list_del(&sec->list);
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free(sec);
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}
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if (elf->name)
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free(elf->name);
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if (elf->fd > 0)
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close(elf->fd);
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if (elf->elf)
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elf_end(elf->elf);
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free(elf);
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}
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