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1 /*
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2 * Copyright 2000 Sun Microsystems, Inc. All Rights Reserved.
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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4 *
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5 * This code is free software; you can redistribute it and/or modify it
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6 * under the terms of the GNU General Public License version 2 only, as
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7 * published by the Free Software Foundation.
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8 *
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9 * This code is distributed in the hope that it will be useful, but WITHOUT
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10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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12 * version 2 for more details (a copy is included in the LICENSE file that
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13 * accompanied this code).
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14 *
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15 * You should have received a copy of the GNU General Public License version
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16 * 2 along with this work; if not, write to the Free Software Foundation,
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17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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18 *
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19 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
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20 * CA 95054 USA or visit www.sun.com if you need additional information or
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21 * have any questions.
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22 *
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23 */
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24
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25 package sun.jvm.hotspot.utilities;
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26
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27 import java.util.*;
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28 import sun.jvm.hotspot.debugger.*;
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29 import sun.jvm.hotspot.memory.*;
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30 import sun.jvm.hotspot.runtime.*;
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31 import sun.jvm.hotspot.types.*;
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32
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33 /** This class determines to the best of its ability, and in a
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34 reasonably robust fashion, whether a given pointer is an intact
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35 oop or not. It does this by checking the integrity of the
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36 metaclass hierarchy. This is only intended for use in the
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37 debugging system. It may provide more resilience to unexpected VM
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38 states than the ObjectHeap code. */
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39
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40 public class RobustOopDeterminator {
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41 private static OopField klassField;
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42
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43 static {
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44 VM.registerVMInitializedObserver(new Observer() {
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45 public void update(Observable o, Object data) {
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46 initialize(VM.getVM().getTypeDataBase());
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47 }
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48 });
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49 }
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50
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51 private static void initialize(TypeDataBase db) {
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52 Type type = db.lookupType("oopDesc");
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53
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54 klassField = type.getOopField("_klass");
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55 }
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56
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57 public static boolean oopLooksValid(OopHandle oop) {
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58 if (oop == null) {
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59 return false;
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60 }
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61 if (!VM.getVM().getUniverse().isIn(oop)) {
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62 return false;
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63 }
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64 try {
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65 for (int i = 0; i < 4; ++i) {
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66 OopHandle next = klassField.getValue(oop);
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67 if (next == null) {
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68 return false;
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69 }
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70 if (next.equals(oop)) {
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71 return true;
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72 }
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73 oop = next;
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74 }
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75 return false;
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76 }
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77 catch (AddressException e) {
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78 return false;
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79 }
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80 }
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81 }
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