ext/libelf/libelf_checksum.c

   1 /*-
   2  * Copyright (c) 2006 Joseph Koshy
   3  * All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that the following conditions
   7  * are met:
   8  * 1. Redistributions of source code must retain the above copyright
   9  *    notice, this list of conditions and the following disclaimer.
  10  * 2. Redistributions in binary form must reproduce the above copyright
  11  *    notice, this list of conditions and the following disclaimer in the
  12  *    documentation and/or other materials provided with the distribution.
  13  *
  14  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
  15  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  16  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  17  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
  18  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  19  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  20  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  21  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  22  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  23  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  24  * SUCH DAMAGE.
  25  */
  26
  27 #include "gelf.h"
  28
  29 #include "_libelf.h"
  30
  31 static unsigned long
  32 _libelf_sum(unsigned long c, const unsigned char *s, size_t size)
  33 {
  34         if (s == NULL || size == 0)
  35                 return (c);
  36
  37         while (size--)
  38                 c += *s++;
  39
  40         return (c);
  41 }
  42
  43 unsigned long
  44 _libelf_checksum(Elf *e, int elfclass)
  45 {
  46         size_t shn;
  47         Elf_Scn *scn;
  48         Elf_Data *d;
  49         unsigned long checksum;
  50         GElf_Ehdr eh;
  51         GElf_Shdr shdr;
  52
  53         if (e == NULL) {
  54                 LIBELF_SET_ERROR(ARGUMENT, 0);
  55                 return (0L);
  56         }
  57
  58         if (e->e_class != elfclass) {
  59                 LIBELF_SET_ERROR(CLASS, 0);
  60                 return (0L);
  61         }
  62
  63         if (gelf_getehdr(e, &eh) == NULL)
  64                 return (0);
  65
  66         /*
  67          * Iterate over all sections in the ELF file, computing the
  68          * checksum along the way.
  69          *
  70          * The first section is always SHN_UNDEF and can be skipped.
  71          * Non-allocatable sections are skipped, as are sections that
  72          * could be affected by utilities such as strip(1).
  73          */
  74
  75         checksum = 0;
  76         for (shn = 1; shn < e->e_u.e_elf.e_nscn; shn++) {
  77                 if ((scn = elf_getscn(e, shn)) == NULL)
  78                         return (0);
  79                 if (gelf_getshdr(scn, &shdr) == NULL)
  80                         return (0);
  81                 if ((shdr.sh_flags & SHF_ALLOC) == 0 ||
  82                     shdr.sh_type == SHT_DYNAMIC ||
  83                     shdr.sh_type == SHT_DYNSYM)
  84                         continue;
  85
  86                 d = NULL;
  87                 while ((d = elf_rawdata(scn, d)) != NULL)
  88                         checksum = _libelf_sum(checksum,
  89                             (unsigned char *) d->d_buf, d->d_size);
  90         }
  91
  92         /*
  93          * Return a 16-bit checksum compatible with Solaris.
  94          */
  95         return (((checksum >> 16) & 0xFFFFUL) + (checksum & 0xFFFFUL));
  96 }