/*      $NetBSD: libelf_checksum.c,v 1.5 2024/03/03 17:37:34 christos Exp $     */

/*-
* Copyright (c) 2006,2008 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 <sys/cdefs.h>

#include <gelf.h>

#include "_libelf.h"

__RCSID("$NetBSD: libelf_checksum.c,v 1.5 2024/03/03 17:37:34 christos Exp $");
ELFTC_VCSID("Id: libelf_checksum.c 3977 2022-05-01 06:45:34Z jkoshy");

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);
}

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, (size_t) d->d_size);
       }

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