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/*
checksum.c - implementation of the elf{32,64}_checksum(3) functions.
Copyright (C) 1995 - 2001 Michael Riepe
This library is free software; you can redistribute it and/or
modify it under the terms of the GNU Library General Public
License as published by the Free Software Foundation; either
version 2 of the License, or (at your option) any later version.
This library 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
Library General Public License for more details.
You should have received a copy of the GNU Library General Public
License along with this library; if not, write to the Free Software
Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA
*/
#include <private.h>
#ifndef lint
static const char rcsid[] = "@(#) $Id: checksum.c,v 1.7 2008/05/23 08:15:34 michael Exp $";
#endif /* lint */
/*
* Compatibility note:
*
* The algorithm used in {elf32,elf64,gelf}_checksum() does not seem to
* be documented. I hope I got it right. My implementation does the
* following:
*
* - skip sections that do not have the SHF_ALLOC flag set
* - skip sections of type SHT_NULL, SHT_NOBITS, SHT_DYNSYM and
* SHT_DYNAMIC
* - add all data bytes from the remaining sections, modulo 2**32
* - add upper and lower half of the result
* - subtract 0xffff if the result is > 0xffff
* - if any error occurs, return 0L
*/
static int
skip_section(Elf_Scn *scn, unsigned cls) {
if (cls == ELFCLASS32) {
Elf32_Shdr *shdr = &scn->s_shdr32;
if (!(shdr->sh_flags & SHF_ALLOC)) {
return 1;
}
switch (shdr->sh_type) {
case SHT_NULL:
case SHT_NOBITS:
/* Solaris seems to ignore these, too */
case SHT_DYNSYM:
case SHT_DYNAMIC:
return 1;
}
}
#if __LIBELF64
else if (cls == ELFCLASS64) {
Elf64_Shdr *shdr = &scn->s_shdr64;
if (!(shdr->sh_flags & SHF_ALLOC)) {
return 1;
}
switch (shdr->sh_type) {
case SHT_NULL:
case SHT_NOBITS:
/* Solaris seems to ignore these, too */
case SHT_DYNSYM:
case SHT_DYNAMIC:
return 1;
}
}
#endif /* __LIBELF64 */
else {
seterr(ERROR_UNIMPLEMENTED);
}
return 0;
}
static long
add_bytes(unsigned char *ptr, size_t len) {
long csum = 0;
while (len--) {
csum += *ptr++;
}
return csum;
}
static long
_elf_csum(Elf *elf) {
long csum = 0;
Elf_Data *data;
Elf_Scn *scn;
if (!elf->e_ehdr && !_elf_cook(elf)) {
/* propagate errors from _elf_cook */
return 0L;
}
seterr(0);
for (scn = elf->e_scn_1; scn; scn = scn->s_link) {
if (scn->s_index == SHN_UNDEF || skip_section(scn, elf->e_class)) {
continue;
}
data = NULL;
while ((data = elf_getdata(scn, data))) {
if (data->d_size) {
if (data->d_buf == NULL) {
seterr(ERROR_NULLBUF);
return 0L;
}
csum += add_bytes(data->d_buf, data->d_size);
}
}
}
if (_elf_errno) {
return 0L;
}
csum = (csum & 0xffff) + ((csum >> 16) & 0xffff);
if (csum > 0xffff) {
csum -= 0xffff;
}
return csum;
}
long
elf32_checksum(Elf *elf) {
if (elf) {
if (elf->e_kind != ELF_K_ELF) {
seterr(ERROR_NOTELF);
}
else if (elf->e_class != ELFCLASS32) {
seterr(ERROR_CLASSMISMATCH);
}
else {
return _elf_csum(elf);
}
}
return 0L;
}
#if __LIBELF64
long
elf64_checksum(Elf *elf) {
if (elf) {
if (elf->e_kind != ELF_K_ELF) {
seterr(ERROR_NOTELF);
}
else if (elf->e_class != ELFCLASS64) {
seterr(ERROR_CLASSMISMATCH);
}
else {
return _elf_csum(elf);
}
}
return 0L;
}
long
gelf_checksum(Elf *elf) {
if (elf) {
if (elf->e_kind != ELF_K_ELF) {
seterr(ERROR_NOTELF);
}
else if (!valid_class(elf->e_class)) {
seterr(ERROR_UNKNOWN_CLASS);
}
else {
return _elf_csum(elf);
}
}
return 0L;
}
#endif /* __LIBELF64 */
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