Write protect executable pages in the VM.

runtime/vm/freelist.h

 // 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.
 
 #ifndef VM_FREELIST_H_
 #define VM_FREELIST_H_
 
 #include "platform/assert.h"
 #include "vm/allocation.h"
 #include "vm/bit_set.h"
 #include "vm/raw_object.h"
 
 namespace dart {
 
 // FreeListElement describes a freelist element.  Smallest FreeListElement is
 // two words in size.  Second word of the raw object is used to keep a next_
 // pointer to chain elements of the list together. For objects larger than the
 // object size encodable in tags field, the size of the element is embedded in
 // the element at the address following the next_ field.
 class FreeListElement {
  public:
+  // Maximum header size is three words (tags, next, and size).
+  static const intptr_t kHeaderSize = 3 * kWordSize;
+
   FreeListElement* next() const {
     return next_;
   }
+  uword next_address() const {
+    return reinterpret_cast<uword>(&next_);
+  }
 
   void set_next(FreeListElement* next) {
     next_ = next;
   }
 
   intptr_t Size() {
     intptr_t size = RawObject::SizeTag::decode(tags_);
     if (size != 0) return size;
     return *SizeAddress();
   }
@@ skipping 33 matching lines @@
   DISALLOW_ALLOCATION();
   DISALLOW_IMPLICIT_CONSTRUCTORS(FreeListElement);
 };
 
 
 class FreeList {
  public:
   FreeList();
   ~FreeList();
 
-  uword TryAllocate(intptr_t size);
+  uword TryAllocate(intptr_t size, bool is_protected);
   void Free(uword addr, intptr_t size);
 
   void Reset();
 
   intptr_t Length(int index) const;
 
   void Print() const;
 
  private:
   static const int kNumLists = 128;
 
   static intptr_t IndexForSize(intptr_t size);
 
   void EnqueueElement(FreeListElement* element, intptr_t index);
   FreeListElement* DequeueElement(intptr_t index);
 
-  void SplitElementAfterAndEnqueue(FreeListElement* element, intptr_t size);
+  void SplitElementAfterAndEnqueue(FreeListElement* element,
+                                   intptr_t size,
+                                   bool is_protected);
 
   void PrintSmall() const;
   void PrintLarge() const;
 
   BitSet<kNumLists> free_map_;
 
   FreeListElement* free_lists_[kNumLists + 1];
 
   DISALLOW_COPY_AND_ASSIGN(FreeList);
 };
 
 }  // namespace dart
 
 #endif  // VM_FREELIST_H_