glibc/sysdeps/generic/dl-osinfo.h

/* Operating system specific code for generic dynamic loader functions.
   Copyright (C) 2009, 2011 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, see
   <http://www.gnu.org/licenses/>.  */

#include <endian.h>
#include <stdint.h>

static inline uintptr_t __attribute__ ((always_inline))
_dl_setup_stack_chk_guard (void *dl_random)
{
  union
  {
    uintptr_t num;
    unsigned char bytes[sizeof (uintptr_t)];
  } ret = { 0 };

  if (dl_random == NULL)
    {
      ret.bytes[sizeof (ret) - 1] = 255;
      ret.bytes[sizeof (ret) - 2] = '\n';
    }
  else
    {
      memcpy (ret.bytes, dl_random, sizeof (ret));
#if BYTE_ORDER == LITTLE_ENDIAN
      ret.num &= ~(uintptr_t) 0xff;
#elif BYTE_ORDER == BIG_ENDIAN
      ret.num &= ~((uintptr_t) 0xff << (8 * (sizeof (ret) - 1)));
#else
# error "BYTE_ORDER unknown"
#endif
    }
  return ret.num;
}

static inline uintptr_t __attribute__ ((always_inline))
_dl_setup_pointer_guard (void *dl_random, uintptr_t stack_chk_guard)
{
  uintptr_t ret;
  if (dl_random == NULL)
    ret = stack_chk_guard;
  else
    memcpy (&ret, (char *) dl_random + sizeof (ret), sizeof (ret));
  return ret;
}