OpenWrt – Rev 1
?pathlinks?
/* http://www.muppetlabs.com/~breadbox/software/elfkickers.html */
/* sstrip: Copyright (C) 1999-2001 by Brian Raiter, under the GNU
* General Public License. No warranty. See COPYING for details.
*
* Aug 23, 2004 Hacked by Manuel Novoa III <mjn3@codepoet.org> to
* handle targets of different endianness and/or elf class, making
* it more useful in a cross-devel environment.
*/
/* ============== original README ===================
*
* sstrip is a small utility that removes the contents at the end of an
* ELF file that are not part of the program's memory image.
*
* Most ELF executables are built with both a program header table and a
* section header table. However, only the former is required in order
* for the OS to load, link and execute a program. sstrip attempts to
* extract the ELF header, the program header table, and its contents,
* leaving everything else in the bit bucket. It can only remove parts of
* the file that occur at the end, after the parts to be saved. However,
* this almost always includes the section header table, and occasionally
* a few random sections that are not used when running a program.
*
* It should be noted that the GNU bfd library is (understandably)
* dependent on the section header table as an index to the file's
* contents. Thus, an executable file that has no section header table
* cannot be used with gdb, objdump, or any other program based upon the
* bfd library, at all. In fact, the program will not even recognize the
* file as a valid executable. (This limitation is noted in the source
* code comments for bfd, and is marked "FIXME", so this may change at
* some future date. However, I would imagine that it is a pretty
* low-priority item, as executables without a section header table are
* rare in the extreme.) This probably also explains why strip doesn't
* offer the option to do this.
*
* Shared library files may also have their section header table removed.
* Such a library will still function; however, it will no longer be
* possible for a compiler to link a new program against it.
*
* As an added bonus, sstrip also tries to removes trailing zero bytes
* from the end of the file. (This normally cannot be done with an
* executable that has a section header table.)
*
* sstrip is a very simplistic program. It depends upon the common
* practice of putting the parts of the file that contribute to the
* memory image at the front, and the remaining material at the end. This
* permits it to discard the latter material without affecting file
* offsets and memory addresses in what remains. Of course, the ELF
* standard permits files to be organized in almost any order, so if a
* pathological linker decided to put its section headers at the top,
* sstrip would be useless on such executables.
*/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <unistd.h>
#include <fcntl.h>
#include <elf.h>
#include <byteswap.h>
#ifndef TRUE
#define TRUE 1
#define FALSE 0
#endif
/* The name of the program.
*/
static char const *progname;
/* The name of the current file.
*/
static char const *filename;
/* A simple error-handling function. FALSE is always returned for the
* convenience of the caller.
*/
static int err(char const *errmsg)
{
fprintf(stderr, "%s: %s: %s\n", progname, filename, errmsg);
return FALSE;
}
/* A flag to signal the need for endian reversal.
*/
static int do_reverse_endian;
/* Get a value from the elf header, compensating for endianness.
*/
#define EGET(X) \
(__extension__ ({ \
uint64_t __res; \
if (!do_reverse_endian) { \
__res = (X); \
} else if (sizeof(X) == 1) { \
__res = (X); \
} else if (sizeof(X) == 2) { \
__res = bswap_16((X)); \
} else if (sizeof(X) == 4) { \
__res = bswap_32((X)); \
} else if (sizeof(X) == 8) { \
__res = bswap_64((X)); \
} else { \
fprintf(stderr, "%s: %s: EGET failed for size %zu\n", \
progname, filename, sizeof(X)); \
exit(EXIT_FAILURE); \
} \
__res; \
}))
/* Set a value 'Y' in the elf header to 'X', compensating for endianness.
*/
#define ESET(Y,X) \
do if (!do_reverse_endian) { \
Y = (X); \
} else if (sizeof(Y) == 1) { \
Y = (X); \
} else if (sizeof(Y) == 2) { \
Y = bswap_16((uint16_t)(X)); \
} else if (sizeof(Y) == 4) { \
Y = bswap_32((uint32_t)(X)); \
} else if (sizeof(Y) == 8) { \
Y = bswap_64((uint64_t)(X)); \
} else { \
fprintf(stderr, "%s: %s: ESET failed for size %zu\n", \
progname, filename, sizeof(Y)); \
exit(EXIT_FAILURE); \
} while (0)
/* A macro for I/O errors: The given error message is used only when
* errno is not set.
*/
#define ferr(msg) (err(errno ? strerror(errno) : (msg)))
#define HEADER_FUNCTIONS(CLASS) \
\
/* readelfheader() reads the ELF header into our global variable, and \
* checks to make sure that this is in fact a file that we should be \
* munging. \
*/ \
static int readelfheader ## CLASS (int fd, Elf ## CLASS ## _Ehdr *ehdr) \
{ \
if (read(fd, ((char *)ehdr)+EI_NIDENT, sizeof(*ehdr) - EI_NIDENT) \
!= sizeof(*ehdr) - EI_NIDENT) \
return ferr("missing or incomplete ELF header."); \
\
/* Verify the sizes of the ELF header and the program segment \
* header table entries. \
*/ \
if (EGET(ehdr->e_ehsize) != sizeof(Elf ## CLASS ## _Ehdr)) \
return err("unrecognized ELF header size."); \
if (EGET(ehdr->e_phentsize) != sizeof(Elf ## CLASS ## _Phdr)) \
return err("unrecognized program segment header size."); \
\
/* Finally, check the file type. \
*/ \
if (EGET(ehdr->e_type) != ET_EXEC && EGET(ehdr->e_type) != ET_DYN) \
return err("not an executable or shared-object library."); \
\
return TRUE; \
} \
\
/* readphdrtable() loads the program segment header table into memory. \
*/ \
static int readphdrtable ## CLASS (int fd, Elf ## CLASS ## _Ehdr const *ehdr, \
Elf ## CLASS ## _Phdr **phdrs) \
{ \
size_t size; \
\
if (!EGET(ehdr->e_phoff) || !EGET(ehdr->e_phnum) \
) return err("ELF file has no program header table."); \
\
size = EGET(ehdr->e_phnum) * sizeof **phdrs; \
if (!(*phdrs = malloc(size))) \
return err("Out of memory!"); \
\
errno = 0; \
if (read(fd, *phdrs, size) != (ssize_t)size) \
return ferr("missing or incomplete program segment header table."); \
\
return TRUE; \
} \
\
/* getmemorysize() determines the offset of the last byte of the file \
* that is referenced by an entry in the program segment header table. \
* (Anything in the file after that point is not used when the program \
* is executing, and thus can be safely discarded.) \
*/ \
static int getmemorysize ## CLASS (Elf ## CLASS ## _Ehdr const *ehdr, \
Elf ## CLASS ## _Phdr const *phdrs, \
unsigned long *newsize) \
{ \
Elf ## CLASS ## _Phdr const *phdr; \
unsigned long size, n; \
size_t i; \
\
/* Start by setting the size to include the ELF header and the \
* complete program segment header table. \
*/ \
size = EGET(ehdr->e_phoff) + EGET(ehdr->e_phnum) * sizeof *phdrs; \
if (size < sizeof *ehdr) \
size = sizeof *ehdr; \
\
/* Then keep extending the size to include whatever data the \
* program segment header table references. \
*/ \
for (i = 0, phdr = phdrs ; i < EGET(ehdr->e_phnum) ; ++i, ++phdr) { \
if (EGET(phdr->p_type) != PT_NULL) { \
n = EGET(phdr->p_offset) + EGET(phdr->p_filesz); \
if (n > size) \
size = n; \
} \
} \
\
*newsize = size; \
return TRUE; \
} \
\
/* modifyheaders() removes references to the section header table if \
* it was stripped, and reduces program header table entries that \
* included truncated bytes at the end of the file. \
*/ \
static int modifyheaders ## CLASS (Elf ## CLASS ## _Ehdr *ehdr, \
Elf ## CLASS ## _Phdr *phdrs, \
unsigned long newsize) \
{ \
Elf ## CLASS ## _Phdr *phdr; \
size_t i; \
\
/* If the section header table is gone, then remove all references \
* to it in the ELF header. \
*/ \
if (EGET(ehdr->e_shoff) >= newsize) { \
ESET(ehdr->e_shoff,0); \
ESET(ehdr->e_shnum,0); \
ESET(ehdr->e_shentsize,0); \
ESET(ehdr->e_shstrndx,0); \
} \
\
/* The program adjusts the file size of any segment that was \
* truncated. The case of a segment being completely stripped out \
* is handled separately. \
*/ \
for (i = 0, phdr = phdrs ; i < EGET(ehdr->e_phnum) ; ++i, ++phdr) { \
if (EGET(phdr->p_offset) >= newsize) { \
ESET(phdr->p_offset,newsize); \
ESET(phdr->p_filesz,0); \
} else if (EGET(phdr->p_offset) + EGET(phdr->p_filesz) > newsize) { \
ESET(phdr->p_filesz, newsize - EGET(phdr->p_offset)); \
} \
} \
\
return TRUE; \
} \
\
/* commitchanges() writes the new headers back to the original file \
* and sets the file to its new size. \
*/ \
static int commitchanges ## CLASS (int fd, Elf ## CLASS ## _Ehdr const *ehdr, \
Elf ## CLASS ## _Phdr *phdrs, \
unsigned long newsize) \
{ \
size_t n; \
\
/* Save the changes to the ELF header, if any. \
*/ \
if (lseek(fd, 0, SEEK_SET)) \
return ferr("could not rewind file"); \
errno = 0; \
if (write(fd, ehdr, sizeof *ehdr) != sizeof *ehdr) \
return err("could not modify file"); \
\
/* Save the changes to the program segment header table, if any. \
*/ \
if (lseek(fd, EGET(ehdr->e_phoff), SEEK_SET) == (off_t)-1) { \
err("could not seek in file."); \
goto warning; \
} \
n = EGET(ehdr->e_phnum) * sizeof *phdrs; \
if (write(fd, phdrs, n) != (ssize_t)n) { \
err("could not write to file"); \
goto warning; \
} \
\
/* Eleventh-hour sanity check: don't truncate before the end of \
* the program segment header table. \
*/ \
if (newsize < EGET(ehdr->e_phoff) + n) \
newsize = EGET(ehdr->e_phoff) + n; \
\
/* Chop off the end of the file. \
*/ \
if (ftruncate(fd, newsize)) { \
err("could not resize file"); \
goto warning; \
} \
\
return TRUE; \
\
warning: \
return err("ELF file may have been corrupted!"); \
}
/* First elements of Elf32_Ehdr and Elf64_Ehdr are common.
*/
static int readelfheaderident(int fd, Elf32_Ehdr *ehdr)
{
errno = 0;
if (read(fd, ehdr, EI_NIDENT) != EI_NIDENT)
return ferr("missing or incomplete ELF header.");
/* Check the ELF signature.
*/
if (!(ehdr->e_ident[EI_MAG0] == ELFMAG0 &&
ehdr->e_ident[EI_MAG1] == ELFMAG1 &&
ehdr->e_ident[EI_MAG2] == ELFMAG2 &&
ehdr->e_ident[EI_MAG3] == ELFMAG3))
{
err("missing ELF signature.");
return -1;
}
/* Compare the file's class and endianness with the program's.
*/
#if __BYTE_ORDER == __LITTLE_ENDIAN
if (ehdr->e_ident[EI_DATA] == ELFDATA2LSB) {
do_reverse_endian = 0;
} else if (ehdr->e_ident[EI_DATA] == ELFDATA2MSB) {
/* fprintf(stderr, "ELF file has different endianness.\n"); */
do_reverse_endian = 1;
}
#elif __BYTE_ORDER == __BIG_ENDIAN
if (ehdr->e_ident[EI_DATA] == ELFDATA2LSB) {
/* fprintf(stderr, "ELF file has different endianness.\n"); */
do_reverse_endian = 1;
} else if (ehdr->e_ident[EI_DATA] == ELFDATA2MSB) {
do_reverse_endian = 0;
}
#else
#error unkown endianness
#endif
else {
err("Unsupported endianness");
return -1;
}
/* Check the target architecture.
*/
/* if (EGET(ehdr->e_machine) != ELF_ARCH) { */
/* /\* return err("ELF file created for different architecture."); *\/ */
/* fprintf(stderr, "ELF file created for different architecture.\n"); */
/* } */
return ehdr->e_ident[EI_CLASS];
}
HEADER_FUNCTIONS(32)
HEADER_FUNCTIONS(64)
/* truncatezeros() examines the bytes at the end of the file's
* size-to-be, and reduces the size to exclude any trailing zero
* bytes.
*/
static int truncatezeros(int fd, unsigned long *newsize)
{
unsigned char contents[1024];
unsigned long size, n;
size = *newsize;
do {
n = sizeof contents;
if (n > size)
n = size;
if (lseek(fd, size - n, SEEK_SET) == (off_t)-1)
return ferr("cannot seek in file.");
if (read(fd, contents, n) != (ssize_t)n)
return ferr("cannot read file contents");
while (n && !contents[--n])
--size;
} while (size && !n);
/* Sanity check.
*/
if (!size)
return err("ELF file is completely blank!");
*newsize = size;
return TRUE;
}
/* main() loops over the cmdline arguments, leaving all the real work
* to the other functions.
*/
int main(int argc, char *argv[])
{
int fd;
union {
Elf32_Ehdr ehdr32;
Elf64_Ehdr ehdr64;
} e;
union {
Elf32_Phdr *phdrs32;
Elf64_Phdr *phdrs64;
} p;
unsigned long newsize;
char **arg;
int failures = 0;
if (argc < 2 || argv[1][0] == '-') {
printf("Usage: sstrip FILE...\n"
"sstrip discards all nonessential bytes from an executable.\n\n"
"Version 2.0-X Copyright (C) 2000,2001 Brian Raiter.\n"
"Cross-devel hacks Copyright (C) 2004 Manuel Novoa III.\n"
"This program is free software, licensed under the GNU\n"
"General Public License. There is absolutely no warranty.\n");
return EXIT_SUCCESS;
}
progname = argv[0];
for (arg = argv + 1 ; *arg != NULL ; ++arg) {
filename = *arg;
fd = open(*arg, O_RDWR);
if (fd < 0) {
ferr("can't open");
++failures;
continue;
}
switch (readelfheaderident(fd, &e.ehdr32)) {
case ELFCLASS32:
if (!(readelfheader32(fd, &e.ehdr32) &&
readphdrtable32(fd, &e.ehdr32, &p.phdrs32) &&
getmemorysize32(&e.ehdr32, p.phdrs32, &newsize) &&
truncatezeros(fd, &newsize) &&
modifyheaders32(&e.ehdr32, p.phdrs32, newsize) &&
commitchanges32(fd, &e.ehdr32, p.phdrs32, newsize)))
++failures;
break;
case ELFCLASS64:
if (!(readelfheader64(fd, &e.ehdr64) &&
readphdrtable64(fd, &e.ehdr64, &p.phdrs64) &&
getmemorysize64(&e.ehdr64, p.phdrs64, &newsize) &&
truncatezeros(fd, &newsize) &&
modifyheaders64(&e.ehdr64, p.phdrs64, newsize) &&
commitchanges64(fd, &e.ehdr64, p.phdrs64, newsize)))
++failures;
break;
default:
++failures;
break;
}
close(fd);
}
return failures ? EXIT_FAILURE : EXIT_SUCCESS;
}