1 /*
   2  * Copyright (c) 2011, 2016, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
  21  * questions.
  22  *
  23  */
  24 
  25 package sun.jvm.hotspot.oops;
  26 
  27 import java.util.*;
  28 
  29 import sun.jvm.hotspot.debugger.*;
  30 import sun.jvm.hotspot.memory.*;
  31 import sun.jvm.hotspot.runtime.*;
  32 import sun.jvm.hotspot.types.AddressField;
  33 import sun.jvm.hotspot.types.Type;
  34 import sun.jvm.hotspot.types.TypeDataBase;
  35 import sun.jvm.hotspot.utilities.*;
  36 
  37 /** A utility class encapsulating useful oop operations */
  38 
  39 // initialize fields for java.lang.Class
  40 public class java_lang_Class {
  41 
  42   // java.lang.Class fields
  43   static int klassOffset;
  44   static IntField oopSizeField;
  45 
  46   static {
  47     VM.registerVMInitializedObserver(new Observer() {
  48         public void update(Observable o, Object data) {
  49           initialize(VM.getVM().getTypeDataBase());
  50         }
  51       });
  52   }
  53 
  54   private static synchronized void initialize(TypeDataBase db) {
  55     // klass and oop_size are HotSpot magic fields and hence we can't
  56     // find them from InstanceKlass for java.lang.Class.
  57     Type jlc = db.lookupType("java_lang_Class");
  58     klassOffset = (int) jlc.getCIntegerField("_klass_offset").getValue();
  59     int oopSizeOffset = (int) jlc.getCIntegerField("_oop_size_offset").getValue();
  60     oopSizeField = new IntField(new NamedFieldIdentifier("oop_size"), oopSizeOffset, true);
  61   }
  62 
  63   /** get Klass* field at offset hc_klass_offset from a java.lang.Class object */
  64   public static Klass asKlass(Oop aClass) {
  65     return (Klass)Metadata.instantiateWrapperFor(aClass.getHandle().getAddressAt(klassOffset));
  66   }
  67 
  68   /** get oop_size field at offset oop_size_offset from a java.lang.Class object */
  69   public static long getOopSize(Oop aClass) {
  70     return java_lang_Class.oopSizeField.getValue(aClass);
  71   }
  72 }