support/next_to_fault.c

   1 /* Memory allocation next to an unmapped page.
   2    Copyright (C) 2017-2020 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 <support/check.h>
  20 #include <support/next_to_fault.h>
  21 #include <support/xunistd.h>
  22 #include <sys/mman.h>
  23 #include <sys/param.h>
  24
  25 struct support_next_to_fault
  26 support_next_to_fault_allocate (size_t size)
  27 {
  28   long page_size = sysconf (_SC_PAGE_SIZE);
  29   TEST_VERIFY_EXIT (page_size > 0);
  30   struct support_next_to_fault result;
  31   result.region_size = roundup (size, page_size) + page_size;
  32   if (size + page_size <= size || result.region_size <= size)
  33     FAIL_EXIT1 ("support_next_to_fault_allocate (%zu): overflow", size);
  34   result.region_start
  35     = xmmap (NULL, result.region_size, PROT_READ | PROT_WRITE,
  36              MAP_PRIVATE | MAP_ANONYMOUS, -1);
  37   /* Unmap the page after the allocation.  */
  38   xmprotect (result.region_start + (result.region_size - page_size),
  39              page_size, PROT_NONE);
  40   /* Align the allocation within the region so that it ends just
  41      before the PROT_NONE page.  */
  42   result.buffer = result.region_start + result.region_size - page_size - size;
  43   result.length = size;
  44   return result;
  45 }
  46
  47 void
  48 support_next_to_fault_free (struct support_next_to_fault *ntf)
  49 {
  50   xmunmap (ntf->region_start, ntf->region_size);
  51   *ntf = (struct support_next_to_fault) { NULL, };
  52 }