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