blob: cc56e7ac8122820bef4350c246b809b9ec2f9c0b [file] [log] [blame]
/*
* 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)
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_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, &sections_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;
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->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 && sym->len >= s->len) {
entry = tmp;
break;
}
}
list_add(&sym->list, entry);
hash_add(sym->sec->symbol_hash, &sym->hash, sym->idx);
}
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);
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_open(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 file %s\n", name);
perror("open");
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;
struct 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 */
shstrtab = find_section_by_name(elf, ".shstrtab");
if (!shstrtab) {
WARN("can't find .shstrtab 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);
}