1  /* Operating system specific code for generic dynamic loader functions.  Linux.
       2     Copyright (C) 2000-2023 Free Software Foundation, Inc.
       3     This file is part of the GNU C Library.
       4  
       5     The GNU C Library is free software; you can redistribute it and/or
       6     modify it under the terms of the GNU Lesser General Public
       7     License as published by the Free Software Foundation; either
       8     version 2.1 of the License, or (at your option) any later version.
       9  
      10     The GNU C Library is distributed in the hope that it will be useful,
      11     but WITHOUT ANY WARRANTY; without even the implied warranty of
      12     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
      13     Lesser General Public License for more details.
      14  
      15     You should have received a copy of the GNU Lesser General Public
      16     License along with the GNU C Library; if not, see
      17     <https://www.gnu.org/licenses/>.  */
      18  
      19  #include <dl-sysdep.h>
      20  #include <endian.h>
      21  #include <fcntl.h>
      22  #include <stdint.h>
      23  #include <not-cancel.h>
      24  
      25  static inline uintptr_t __attribute__ ((always_inline))
      26  _dl_setup_stack_chk_guard (void *dl_random)
      27  {
      28    union
      29    {
      30      uintptr_t num;
      31      unsigned char bytes[sizeof (uintptr_t)];
      32    } ret;
      33  
      34    /* We need in the moment only 8 bytes on 32-bit platforms and 16
      35       bytes on 64-bit platforms.  Therefore we can use the data
      36       directly and not use the kernel-provided data to seed a PRNG.  */
      37    memcpy (ret.bytes, dl_random, sizeof (ret));
      38  #if BYTE_ORDER == LITTLE_ENDIAN
      39    ret.num &= ~(uintptr_t) 0xff;
      40  #elif BYTE_ORDER == BIG_ENDIAN
      41    ret.num &= ~((uintptr_t) 0xff << (8 * (sizeof (ret) - 1)));
      42  #else
      43  # error "BYTE_ORDER unknown"
      44  #endif
      45    return ret.num;
      46  }
      47  
      48  static inline uintptr_t __attribute__ ((always_inline))
      49  _dl_setup_pointer_guard (void *dl_random, uintptr_t stack_chk_guard)
      50  {
      51    uintptr_t ret;
      52    memcpy (&ret, (char *) dl_random + sizeof (ret), sizeof (ret));
      53    return ret;
      54  }