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/* Memory allocation either before or after an unmapped page.
Copyright (C) 2017-2025 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 <stdbool.h>
#include <support/check.h>
#include <support/next_to_fault.h>
#include <support/xunistd.h>
#include <sys/mman.h>
#include <sys/param.h>
static struct support_next_to_fault
support_next_to_fault_allocate_any (size_t size, bool fault_after_alloc)
{
long page_size = sysconf (_SC_PAGE_SIZE);
long protect_offset = 0;
long buffer_offset = 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 ("%s (%zu): overflow", __func__, size);
result.region_start
= xmmap (NULL, result.region_size, PROT_READ | PROT_WRITE,
MAP_PRIVATE | MAP_ANONYMOUS, -1);
if (fault_after_alloc)
{
protect_offset = result.region_size - page_size;
buffer_offset = protect_offset - size;
}
/* Unmap the page before or after the allocation. */
xmprotect (result.region_start + protect_offset, page_size, PROT_NONE);
/* Align the allocation within the region so that it starts after or ends
just before the PROT_NONE page. */
result.buffer = result.region_start + buffer_offset;
result.length = size;
return result;
}
/* Unmapped a page after the buffer */
struct support_next_to_fault
support_next_to_fault_allocate (size_t size)
{
return support_next_to_fault_allocate_any (size, true);
}
/* Unmapped a page before the buffer */
struct support_next_to_fault
support_next_to_fault_allocate_before (size_t size)
{
return support_next_to_fault_allocate_any (size, false);
}
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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