--- a/hotspot/agent/src/share/classes/sun/jvm/hotspot/oops/Instance.java	Fri Apr 11 09:56:35 2008 -0400
+++ b/hotspot/agent/src/share/classes/sun/jvm/hotspot/oops/Instance.java	Sun Apr 13 17:43:42 2008 -0400
@@ -40,15 +40,26 @@
         }
       });
   }
+  private static long typeSize;
 
   private static synchronized void initialize(TypeDataBase db) throws WrongTypeException {
     Type type = db.lookupType("instanceOopDesc");
+    typeSize = type.getSize();
   }
 
   Instance(OopHandle handle, ObjectHeap heap) {
     super(handle, heap);
   }
 
+  // Returns header size in bytes.
+  public static long getHeaderSize() {
+    if (VM.getVM().isCompressedOopsEnabled()) {
+      return typeSize - VM.getVM().getIntSize();
+    } else {
+      return typeSize;
+    }
+  }
+
   public boolean isInstance()          { return true; }
 
   public void iterateFields(OopVisitor visitor, boolean doVMFields) {