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/* go-trampoline.c -- allocate a trampoline for a nested function.

   Copyright 2009 The Go Authors. All rights reserved.

   Use of this source code is governed by a BSD-style

   license that can be found in the LICENSE file.  */

#include "config.h"

#include <stddef.h>

#include <stdint.h>

#include <unistd.h>

#ifdef HAVE_SYS_MMAN_H

#include <sys/mman.h>

#endif

#include "go-alloc.h"

#include "go-assert.h"

/* In order to build a trampoline we need space which is both writable

   and executable.  We currently just allocate a whole page.  This

   needs to be more system dependent.  */

void *

__go_allocate_trampoline (uintptr_t size, void *closure)

{

  unsigned int page_size;

  void *ret;

  size_t off;

  page_size = getpagesize ();

  __go_assert (page_size >= size);

  ret = __go_alloc (2 * page_size - 1);

  ret = (void *) (((uintptr_t) ret + page_size - 1)

                  & ~ ((uintptr_t) page_size - 1));

  /* Because the garbage collector only looks at correct address

     offsets, we need to ensure that it will see the closure

     address.  */

  off = ((size + sizeof (void *) - 1) / sizeof (void *)) * sizeof (void *);

  __go_assert (size + off + sizeof (void *) <= page_size);

  __builtin_memcpy (ret + off, &closure, sizeof (void *));

#ifdef HAVE_SYS_MMAN_H

  {

    int i;

    i = mprotect (ret, size, PROT_READ | PROT_WRITE | PROT_EXEC);

    __go_assert (i == 0);

  }

#endif

  return ret;

}