Write protect executable pages in the VM.

runtime/vm/assembler.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_ASSEMBLER_H_
 #define VM_ASSEMBLER_H_
 
 #include "platform/assert.h"
 #include "vm/allocation.h"
 #include "vm/globals.h"
@@ skipping 35 matching lines @@
 };
 
 
 // Assembler fixups are positions in generated code that hold relocation
 // information that needs to be processed before finalizing the code
 // into executable memory.
 class AssemblerFixup : public ZoneAllocated {
  public:
   virtual void Process(const MemoryRegion& region, intptr_t position) = 0;
 
+  virtual bool IsPointerOffset() const = 0;
+
   // It would be ideal if the destructor method could be made private,
   // but the g++ compiler complains when this is subclassed.
   virtual ~AssemblerFixup() { UNREACHABLE(); }
 
  private:
   AssemblerFixup* previous_;
   intptr_t position_;
 
   AssemblerFixup* previous() const { return previous_; }
   void set_previous(AssemblerFixup* previous) { previous_ = previous; }
@@ skipping 45 matching lines @@
   // Emit an object pointer directly in the code.
   void EmitObject(const Object& object);
 
   // Emit a fixup at the current location.
   void EmitFixup(AssemblerFixup* fixup) {
     fixup->set_previous(fixup_);
     fixup->set_position(Size());
     fixup_ = fixup;
   }
 
+  // Count the fixups that produce a pointer offset, without processing
+  // the fixups.
+  intptr_t CountPointerOffsets() const;
+
   // Get the size of the emitted code.
   intptr_t Size() const { return cursor_ - contents_; }
   uword contents() const { return contents_; }
 
   // Copy the assembled instructions into the specified memory block
   // and apply all fixups.
   void FinalizeInstructions(const MemoryRegion& region);
 
   // To emit an instruction to the assembler buffer, the EnsureCapacity helper
   // must be used to guarantee that the underlying data area is big enough to
@@ skipping 80 matching lines @@
 #include "vm/assembler_x64.h"
 #elif defined(TARGET_ARCH_ARM)
 #include "vm/assembler_arm.h"
 #elif defined(TARGET_ARCH_MIPS)
 #include "vm/assembler_mips.h"
 #else
 #error Unknown architecture.
 #endif
 
 #endif  // VM_ASSEMBLER_H_