sstrip.c

UPX 源代码

/* 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 <[e-mail]> 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    <endian.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 %ld\n", \
                    progname, filename, (long) 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 %ld\n", \
                    progname, filename, (long) 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) \
        != (ssize_t)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 \