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/* Implement __enable_execute_stack using mprotect(2).

   Copyright (C) 2011, 2012 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 __FreeBSD__

#include <sys/sysctl.h>

static void __attribute__ ((constructor))

check_enabling (void)

{

  int prot = 0;

  size_t len = sizeof (prot);

  sysctlbyname ("kern.stackprot", &prot, &len, NULL, 0);

  if (prot != STACK_PROT_RWX)

    need_enable_exec_stack = 1;

}

#elif 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 ();

    }

}