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/* Implement __enable_execute_stack using mprotect(2).
Copyright (C) 2011-2021 Free Software Foundation, Inc.
This file is part of GCC.
GCC is free software; you can redistribute it and/or modify it under
the terms of the GNU General Public License as published by the Free
Software Foundation; either version 3, or (at your option) any later
version.
GCC 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 General Public License
for more details.
Under Section 7 of GPL version 3, you are granted additional
permissions described in the GCC Runtime Library Exception, version
3.1, as published by the Free Software Foundation.
You should have received a copy of the GNU General Public License and
a copy of the GCC Runtime Library Exception along with this program;
see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
<http://www.gnu.org/licenses/>. */
#include <sys/mman.h>
#include <unistd.h>
#include <stdlib.h>
#define STACK_PROT_RWX (PROT_READ | PROT_WRITE | PROT_EXEC)
static int need_enable_exec_stack;
static void check_enabling (void) __attribute__ ((unused));
extern void __enable_execute_stack (void *);
#if defined __sun__ && defined __svr4__
static void __attribute__ ((constructor))
check_enabling (void)
{
int prot = (int) sysconf (_SC_STACK_PROT);
if (prot != STACK_PROT_RWX)
need_enable_exec_stack = 1;
}
#else
/* There is no way to query the execute permission of the stack, so
we always issue the mprotect() call. */
static int need_enable_exec_stack = 1;
#endif
/* Attempt to turn on access permissions for the stack. Unfortunately it
is not possible to make this namespace-clean.*/
void
__enable_execute_stack (void *addr)
{
if (!need_enable_exec_stack)
return;
else
{
static long size, mask;
if (size == 0) {
size = getpagesize ();
mask = ~(size - 1);
}
char *page = (char *) (((long) addr) & mask);
char *end = (char *)
((((long) (addr + __LIBGCC_TRAMPOLINE_SIZE__)) & mask) + size);
if (mprotect (page, end - page, STACK_PROT_RWX) < 0)
/* Note that no errors should be emitted by this code; it is
considered dangerous for library calls to send messages to
stdout/stderr. */
abort ();
}
}
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