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/* Memory allocation next to an unmapped page.
Copyright (C) 2017-2021 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
<https://www.gnu.org/licenses/>. */
#include <support/check.h>
#include <support/next_to_fault.h>
#include <support/xunistd.h>
#include <sys/mman.h>
#include <sys/param.h>
struct support_next_to_fault
support_next_to_fault_allocate (size_t size)
{
long page_size = sysconf (_SC_PAGE_SIZE);
TEST_VERIFY_EXIT (page_size > 0);
struct support_next_to_fault result;
result.region_size = roundup (size, page_size) + page_size;
if (size + page_size <= size || result.region_size <= size)
FAIL_EXIT1 ("support_next_to_fault_allocate (%zu): overflow", size);
result.region_start
= xmmap (NULL, result.region_size, PROT_READ | PROT_WRITE,
MAP_PRIVATE | MAP_ANONYMOUS, -1);
/* Unmap the page after the allocation. */
xmprotect (result.region_start + (result.region_size - page_size),
page_size, PROT_NONE);
/* Align the allocation within the region so that it ends just
before the PROT_NONE page. */
result.buffer = result.region_start + result.region_size - page_size - size;
result.length = size;
return result;
}
void
support_next_to_fault_free (struct support_next_to_fault *ntf)
{
xmunmap (ntf->region_start, ntf->region_size);
*ntf = (struct support_next_to_fault) { NULL, };
}
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