ext/libelf/libelf_checksum.c

/*-
 * Copyright (c) 2006 Joseph Koshy
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include "gelf.h"

#include "_libelf.h"

static unsigned long
_libelf_sum(unsigned long c, const unsigned char *s, size_t size)
{
        if (s == NULL || size == 0)
                return (c);

        while (size--)
                c += *s++;

        return (c);
}

unsigned long
_libelf_checksum(Elf *e, int elfclass)
{
        size_t shn;
        Elf_Scn *scn;
        Elf_Data *d;
        unsigned long checksum;
        GElf_Ehdr eh;
        GElf_Shdr shdr;

        if (e == NULL) {
                LIBELF_SET_ERROR(ARGUMENT, 0);
                return (0L);
        }

        if (e->e_class != elfclass) {
                LIBELF_SET_ERROR(CLASS, 0);
                return (0L);
        }

        if (gelf_getehdr(e, &eh) == NULL)
                return (0);

        /*
         * Iterate over all sections in the ELF file, computing the
         * checksum along the way.
         *
         * The first section is always SHN_UNDEF and can be skipped.
         * Non-allocatable sections are skipped, as are sections that
         * could be affected by utilities such as strip(1).
         */

        checksum = 0;
        for (shn = 1; shn < e->e_u.e_elf.e_nscn; shn++) {
                if ((scn = elf_getscn(e, shn)) == NULL)
                        return (0);
                if (gelf_getshdr(scn, &shdr) == NULL)
                        return (0);
                if ((shdr.sh_flags & SHF_ALLOC) == 0 ||
                    shdr.sh_type == SHT_DYNAMIC ||
                    shdr.sh_type == SHT_DYNSYM)
                        continue;

                d = NULL;
                while ((d = elf_rawdata(scn, d)) != NULL)
                        checksum = _libelf_sum(checksum,
                            (unsigned char *) d->d_buf, d->d_size);
        }

        /*
         * Return a 16-bit checksum compatible with Solaris.
         */
        return (((checksum >> 16) & 0xFFFFUL) + (checksum & 0xFFFFUL));
}