src/jdk.hotspot.agent/share/classes/sun/jvm/hotspot/debugger/DebuggerBase.java

@@ -22,10 +22,13 @@
   *
   */
  
  package sun.jvm.hotspot.debugger;
  
+ import sun.jvm.hotspot.oops.Mark;
+ import sun.jvm.hotspot.runtime.VM;
+ 
  /** <P> DebuggerBase is a recommended base class for debugger
      implementations. It can use a PageCache to cache data from the
      target process. Note that this class would not be suitable if the
      system were used to reflect upon itself; it would never be safe to
      store the value in an OopHandle in anything but an OopHandle.

@@ -392,11 +395,19 @@
      return value;
    }
  
    protected long readCompKlassAddressValue(long address)
      throws UnmappedAddressException, UnalignedAddressException {
-     long value = readCInteger(address, getKlassPtrSize(), true);
+     long value;
+     if (VM.getVM().isCompactObjectHeadersEnabled()) {
+       // With compact headers, the compressed Klass* is currently read from the mark
+       // word. We need to load the whole mark, and shift the upper parts.
+       value = readCInteger(address, machDesc.getAddressSize(), true);
+       value = value >>> Mark.getKlassShift();
+     } else {
+       value = readCInteger(address, getKlassPtrSize(), true);
+     }
      if (value != 0) {
        value = (long)(narrowKlassBase + (long)(value << narrowKlassShift));
      }
      return value;
    }