Write protect executable pages in the VM.

runtime/vm/virtual_memory.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/virtual_memory.h"
 
 #include "platform/assert.h"
 #include "platform/utils.h"
 
 namespace dart {
 
+bool VirtualMemory::InSamePage(uword address0, uword address1) {
+  return (Utils::RoundDown(address0, PageSize()) ==
+          Utils::RoundDown(address1, PageSize()));
+}
+
+
 VirtualMemory* VirtualMemory::ReserveAligned(intptr_t size,
                                              intptr_t alignment) {
   ASSERT((size & (PageSize() - 1)) == 0);
   ASSERT(Utils::IsPowerOfTwo(alignment));
   ASSERT(alignment >= PageSize());
   VirtualMemory* result = VirtualMemory::Reserve(size + alignment);
   if (result == NULL) {
     FATAL("Out of memory.\n");
   }
   uword start = result->start();
@@ skipping 12 matching lines @@
     FreeSubSegment(address(), split);
     region_.Subregion(region_, split, size() - split);
   }
   ASSERT(new_size <= size());
   FreeSubSegment(reinterpret_cast<void*>(start() + new_size),
                  size() - new_size);
   region_.Subregion(region_, 0, new_size);
 }
 
 }  // namespace dart