mirror of
https://sourceware.org/git/glibc.git
synced 2024-11-15 17:40:06 +00:00
60 lines
2.2 KiB
C
60 lines
2.2 KiB
C
/* System-specific malloc support functions. Linux version.
|
|
Copyright (C) 2012-2016 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
|
|
<http://www.gnu.org/licenses/>. */
|
|
|
|
#include <fcntl.h>
|
|
#include <not-cancel.h>
|
|
|
|
/* The Linux kernel overcommits address space by default and if there is not
|
|
enough memory available, it uses various parameters to decide the process to
|
|
kill. It is however possible to disable or curb this overcommit behavior
|
|
by setting the proc sysctl vm.overcommit_memory to the value '2' and with
|
|
that, a process is only allowed to use the maximum of a pre-determined
|
|
fraction of the total address space. In such a case, we want to make sure
|
|
that we are judicious with our heap usage as well, and explicitly give away
|
|
the freed top of the heap to reduce our commit charge. See the proc(5) man
|
|
page to know more about overcommit behavior.
|
|
|
|
Other than that, we also force an unmap in a secure exec. */
|
|
static inline bool
|
|
check_may_shrink_heap (void)
|
|
{
|
|
static int may_shrink_heap = -1;
|
|
|
|
if (__builtin_expect (may_shrink_heap >= 0, 1))
|
|
return may_shrink_heap;
|
|
|
|
may_shrink_heap = __libc_enable_secure;
|
|
|
|
if (__builtin_expect (may_shrink_heap == 0, 1))
|
|
{
|
|
int fd = open_not_cancel_2 ("/proc/sys/vm/overcommit_memory",
|
|
O_RDONLY | O_CLOEXEC);
|
|
if (fd >= 0)
|
|
{
|
|
char val;
|
|
ssize_t n = read_not_cancel (fd, &val, 1);
|
|
may_shrink_heap = n > 0 && val == '2';
|
|
close_not_cancel_no_status (fd);
|
|
}
|
|
}
|
|
|
|
return may_shrink_heap;
|
|
}
|
|
|
|
#define HAVE_MREMAP 1
|