tests/altstack.h

   1 /* Some auxiliary stuff for defining an alternate stack.
   2    Copyright (C) 2010  Eric Blake <eblake@redhat.com>
   3    Copyright (C) 2010  Bruno Haible <bruno@clisp.org>
   4
   5    This program is free software; you can redistribute it and/or modify
   6    it under the terms of the GNU General Public License as published by
   7    the Free Software Foundation; either version 2, or (at your option)
   8    any later version.
   9
  10    This program 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
  13    GNU General Public License for more details.
  14
  15    You should have received a copy of the GNU General Public License
  16    along with this program; if not, write to the Free Software Foundation,
  17    Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.  */
  18
  19 #include <string.h> /* for memset */
  20
  21 /* Get uintptr_t.  */
  22 #if HAVE_STDINT_H
  23 # include <stdint.h>
  24 #endif
  25 #if HAVE_INTTYPES_H
  26 # include <inttypes.h>
  27 #endif
  28
  29 #ifndef SIGSTKSZ
  30 # define SIGSTKSZ 16384
  31 #endif
  32
  33 /* glibc says: Users should use SIGSTKSZ as the size of user-supplied
  34    buffers.  We want to detect stack overflow of the alternate stack
  35    in a nicer manner than just crashing, so we overallocate in
  36    comparison to what we hand libsigsegv.  Also, we intentionally hand
  37    an unaligned pointer, to ensure the alternate stack still ends up
  38    aligned.  */
  39 #define MYSTACK_CRUMPLE_ZONE 8192
  40 char mystack_storage[SIGSTKSZ + 2 * MYSTACK_CRUMPLE_ZONE + 31];
  41 char *mystack; /* SIGSTKSZ bytes in the middle of storage. */
  42
  43 static void
  44 prepare_alternate_stack (void)
  45 {
  46   memset (mystack_storage, 's', sizeof mystack_storage);
  47   mystack = (char *) ((uintptr_t) (mystack_storage + MYSTACK_CRUMPLE_ZONE) | 31);
  48 }
  49
  50 static void
  51 check_alternate_stack_no_overflow (void)
  52 {
  53   unsigned int i;
  54
  55   for (i = MYSTACK_CRUMPLE_ZONE; i > 0; i--)
  56     if (*(mystack - i) != 's')
  57       {
  58         printf ("Alternate stack was exceeded by %u bytes!!\n", i);
  59         exit (1);
  60       }
  61   for (i = MYSTACK_CRUMPLE_ZONE; i > 0; i--)
  62     if (*(mystack + SIGSTKSZ - 1 + i) != 's')
  63       {
  64         printf ("Alternate stack was exceeded by %u bytes!!\n", i);
  65         exit (1);
  66       }
  67 }