001 /*
002 * This file is part of the Jikes RVM project (http://jikesrvm.org).
003 *
004 * This file is licensed to You under the Eclipse Public License (EPL);
005 * You may not use this file except in compliance with the License. You
006 * may obtain a copy of the License at
007 *
008 * http://www.opensource.org/licenses/eclipse-1.0.php
009 *
010 * See the COPYRIGHT.txt file distributed with this work for information
011 * regarding copyright ownership.
012 */
013 package org.jikesrvm.objectmodel;
014
015 import org.jikesrvm.VM;
016 import org.jikesrvm.classloader.SpecializedMethodManager;
017
018 /**
019 * Layout the TIB (Type Information Block).
020 * <p>
021 *
022 * <pre>
023 * --------------------------------------------------------------------------------------------
024 * Type Information Block (TIB) Layout Constants
025 * --------------------------------------------------------------------------------------------
026 *
027 * Object[] (type info block) RVMType (class info)
028 * / /
029 * +--------------------+ +--------------+
030 * | TIB pointer | | TIB pointer |
031 * +--------------------+ +--------------+
032 * | status | | status |
033 * +--------------------+ +--------------+
034 * | length | | field0 |
035 * +--------------------+ +--------------+
036 * TIB: 0:| type +------------> | ... |
037 * +--------------------+ +--------------+
038 * 1:| superclass ids +--> | fieldN-1 |
039 * +--------------------+ +--------------+
040 * 2:| implements trits +-->
041 * +--------------------+
042 * 3:| array element TIB +-->
043 * +--------------------+
044 * 4:| iTABLES/IMT +-->
045 * +--------------------+
046 * 5:| specialized 0 +-->
047 * +--------------------+
048 * | ... +-->
049 * +--------------------+
050 * V0:| virtual method 0 +-----+
051 * +--------------------+ |
052 * | ... | | INSTRUCTION[] (machine code)
053 * +--------------------+ | /
054 * VN-1:| virtual method N-1 | | +--------------+
055 * +--------------------+ | | TIB pointer |
056 * | +--------------+
057 * | | status |
058 * | +--------------+
059 * | | length |
060 * | +--------------+
061 * +------->| code0 |
062 * +--------------+
063 * | ... |
064 * +--------------+
065 * | codeN-1 |
066 * +--------------+
067 *
068 * </pre>
069 */
070 public interface TIBLayoutConstants {
071
072 /** Number of slots reserved for interface method pointers. */
073 int IMT_METHOD_SLOTS = VM.BuildForIMTInterfaceInvocation ? 29 : 0;
074
075 /** First slot of TIB points to RVMType (slot 0 in above diagram). */
076 int TIB_TYPE_INDEX = 0;
077
078 /** A vector of ids for classes that this one extends. See
079 DynamicTypeCheck.java */
080 int TIB_SUPERCLASS_IDS_INDEX = TIB_TYPE_INDEX + 1;
081
082 /** Does this class implement the ith interface? See DynamicTypeCheck.java */
083 int TIB_DOES_IMPLEMENT_INDEX = TIB_SUPERCLASS_IDS_INDEX + 1;
084
085 /** The TIB of the elements type of an array (may be {@code null} in fringe cases
086 * when element type couldn't be resolved during array resolution).
087 * Will be {@code null} when not an array.
088 */
089 int TIB_ARRAY_ELEMENT_TIB_INDEX = TIB_DOES_IMPLEMENT_INDEX + 1;
090
091 /**
092 * A pointer to either an ITable or InterfaceMethodTable (IMT)
093 * depending on which dispatch implementation we are using.
094 */
095 int TIB_INTERFACE_DISPATCH_TABLE_INDEX = TIB_ARRAY_ELEMENT_TIB_INDEX + 1;
096
097 /**
098 * A set of 0 or more specialized methods used in the VM such as for GC scanning.
099 */
100 int TIB_FIRST_SPECIALIZED_METHOD_INDEX = TIB_INTERFACE_DISPATCH_TABLE_INDEX + 1;
101
102 /**
103 * Next group of slots point to virtual method code blocks (slots V1..VN in above diagram).
104 */
105 int TIB_FIRST_VIRTUAL_METHOD_INDEX = TIB_FIRST_SPECIALIZED_METHOD_INDEX + SpecializedMethodManager.numSpecializedMethods();
106
107 /**
108 * Special value returned by RVMClassLoader.getFieldOffset() or
109 * RVMClassLoader.getMethodOffset() to indicate fields or methods
110 * that must be accessed via dynamic linking code because their
111 * offset is not yet known or the class's static initializer has not
112 * yet been run.
113 *
114 * We choose a value that will never match a valid jtoc-,
115 * instance-, or virtual method table- offset. Short.MIN_VALUE+1 is
116 * a good value:
117 *
118 * <ul>
119 * <li>the jtoc offsets are aligned and this value should be
120 * too huge to address the table</li>
121 * <li>instance field offsets are always >e; -4</li>
122 * <li>virtual method offsets are always positive w.r.t. TIB pointer</li>
123 * <li>fits into a PowerPC 16bit immediate operand</li>
124 * </ul>
125 */
126 int NEEDS_DYNAMIC_LINK = Short.MIN_VALUE + 1;
127 }
128