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/* Test that free preserves errno.
Copyright (C) 2020-2024 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 <errno.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <stdint.h>
#include <string.h>
#include <sys/mman.h>
#include <support/check.h>
#include <support/support.h>
#include <support/temp_file.h>
#include <support/xunistd.h>
/* The __attribute__ ((weak)) prevents a GCC optimization. Without
it, GCC would "know" that errno is unchanged by calling free (ptr),
when ptr was the result of a malloc call in the same function. */
int __attribute__ ((weak))
get_errno (void)
{
return errno;
}
static int
do_test (void)
{
/* Check that free() preserves errno. */
{
errno = 1789; /* Liberté, égalité, fraternité. */
free (NULL);
TEST_VERIFY (get_errno () == 1789);
}
{ /* Large memory allocations, to force mmap. */
enum { N = 2 };
void * volatile ptrs[N];
size_t i;
for (i = 0; i < N; i++)
ptrs[i] = xmalloc (5318153);
for (i = 0; i < N; i++)
{
errno = 1789;
free (ptrs[i]);
TEST_VERIFY (get_errno () == 1789);
}
}
/* Test a less common code path.
When malloc() is based on mmap(), free() can sometimes call munmap().
munmap() usually succeeds, but fails in a particular situation: when
- it has to unmap the middle part of a VMA, and
- the number of VMAs of a process is limited and the limit is
already reached.
The latter condition is fulfilled on Linux, when the file
/proc/sys/vm/max_map_count exists. For all known Linux versions
the default limit is at most 65536.
*/
#if defined __linux__
if (xopen ("/proc/sys/vm/max_map_count", O_RDONLY, 0) >= 0)
{
/* Preparations. */
size_t pagesize = getpagesize ();
void *firstpage_backup = xmalloc (pagesize);
void *lastpage_backup = xmalloc (pagesize);
/* Allocate a large memory area, as a bumper, so that the MAP_FIXED
allocation later will not overwrite parts of the memory areas
allocated to ld.so or libc.so. */
xmmap (NULL, 0x1000000, PROT_READ, MAP_ANONYMOUS | MAP_PRIVATE, -1);
/* A file descriptor pointing to a regular file. */
int fd = create_temp_file ("tst-free-errno", NULL);
if (fd < 0)
FAIL_EXIT1 ("cannot create temporary file");
/* Do a large memory allocation. */
size_t big_size = 0x1000000;
void * volatile ptr = xmalloc (big_size - 0x100);
char *ptr_aligned = (char *) ((uintptr_t) ptr & ~(pagesize - 1));
/* This large memory allocation allocated a memory area
from ptr_aligned to ptr_aligned + big_size.
Enlarge this memory area by adding a page before and a page
after it. */
memcpy (firstpage_backup, ptr_aligned, pagesize);
memcpy (lastpage_backup, ptr_aligned + big_size - pagesize,
pagesize);
xmmap (ptr_aligned - pagesize, pagesize + big_size + pagesize,
PROT_READ | PROT_WRITE,
MAP_ANONYMOUS | MAP_PRIVATE | MAP_FIXED, -1);
memcpy (ptr_aligned, firstpage_backup, pagesize);
memcpy (ptr_aligned + big_size - pagesize, lastpage_backup,
pagesize);
/* Now add as many mappings as we can.
Stop at 65536, in order not to crash the machine (in case the
limit has been increased by the system administrator). */
for (int i = 0; i < 65536; i++)
if (mmap (NULL, pagesize, PROT_READ, MAP_FILE | MAP_PRIVATE, fd, 0)
== MAP_FAILED)
break;
/* Now the number of VMAs of this process has hopefully attained
its limit. */
errno = 1789;
/* This call to free() is supposed to call
munmap (ptr_aligned, big_size);
which increases the number of VMAs by 1, which is supposed
to fail. */
free (ptr);
TEST_VERIFY (get_errno () == 1789);
}
#endif
return 0;
}
#include <support/test-driver.c>
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