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Java > Open Source Codes > proguard > classfile > editor > VariableRemapper


1 /*
2  * ProGuard -- shrinking, optimization, obfuscation, and preverification
3  * of Java bytecode.
4  *
5  * Copyright (c) 2002-2007 Eric Lafortune (eric@graphics.cornell.edu)
6  *
7  * This program is free software; you can redistribute it and/or modify it
8  * under the terms of the GNU General Public License as published by the Free
9  * Software Foundation; either version 2 of the License, or (at your option)
10  * any later version.
11  *
12  * This program is distributed in the hope that it will be useful, but WITHOUT
13  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
14  * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
15  * more details.
16  *
17  * You should have received a copy of the GNU General Public License along
18  * with this program; if not, write to the Free Software Foundation, Inc.,
19  * 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
20  */
21 package proguard.classfile.editor;
22
23 import proguard.classfile.*;
24 import proguard.classfile.attribute.*;
25 import proguard.classfile.attribute.visitor.*;
26 import proguard.classfile.instruction.*;
27 import proguard.classfile.instruction.visitor.InstructionVisitor;
28 import proguard.classfile.util.SimplifiedVisitor;
29
30 /**
31  * This AttributeVisitor remaps variable indexes in all attributes that it
32  * visits, based on a given index map.
33  *
34  * @author Eric Lafortune
35  */
36 public class VariableRemapper
37 extends SimplifiedVisitor
38 implements AttributeVisitor,
39              InstructionVisitor,
40              LocalVariableInfoVisitor,
41              LocalVariableTypeInfoVisitor
42 {
43     private CodeAttributeEditor codeAttributeEditor = new CodeAttributeEditor();
44
45     private int[] variableMap;
46
47
48     /**
49      * Sets the given mapping of old variable indexes to their new indexes.
50      * Variables that should disappear can be mapped to -1.
51      */
52     public void setVariableMap(int[] variableMap)
53     {
54         this.variableMap = variableMap;
55     }
56
57
58     // Implementations for AttributeVisitor.
59
60     public void visitAnyAttribute(Clazz clazz, Attribute attribute) {}
61
62
63     public void visitCodeAttribute(Clazz clazz, Method method, CodeAttribute codeAttribute)
64     {
65         // Initially, the code attribute editor doesn't contain any changes.
66 codeAttributeEditor.reset(codeAttribute.u4codeLength);
67
68         // Remap the variables of the instructions.
69 codeAttribute.instructionsAccept(clazz, method, this);
70
71         // Apply the code atribute editor.
72 codeAttributeEditor.visitCodeAttribute(clazz, method, codeAttribute);
73
74         // Remap the variables of the attributes.
75 codeAttribute.attributesAccept(clazz, method, this);
76     }
77
78
79     public void visitLocalVariableTableAttribute(Clazz clazz, Method method, CodeAttribute codeAttribute, LocalVariableTableAttribute localVariableTableAttribute)
80     {
81         // Remap the variable references of the local variables.
82 localVariableTableAttribute.localVariablesAccept(clazz, method, codeAttribute, this);
83
84         // Remove local variables that haven't been mapped.
85 localVariableTableAttribute.u2localVariableTableLength =
86             removeEmptyLocalVariables(localVariableTableAttribute.localVariableTable,
87                                       localVariableTableAttribute.u2localVariableTableLength);
88     }
89
90
91     public void visitLocalVariableTypeTableAttribute(Clazz clazz, Method method, CodeAttribute codeAttribute, LocalVariableTypeTableAttribute localVariableTypeTableAttribute)
92     {
93         // Remap the variable references of the local variables.
94 localVariableTypeTableAttribute.localVariablesAccept(clazz, method, codeAttribute, this);
95
96         // Remove local variables that haven't been mapped.
97 localVariableTypeTableAttribute.u2localVariableTypeTableLength =
98             removeEmptyLocalVariableTypes(localVariableTypeTableAttribute.localVariableTypeTable,
99                                           localVariableTypeTableAttribute.u2localVariableTypeTableLength);
100     }
101
102
103     // Implementations for LocalVariableInfoVisitor.
104
105     public void visitLocalVariableInfo(Clazz clazz, Method method, CodeAttribute codeAttribute, LocalVariableInfo localVariableInfo)
106     {
107         localVariableInfo.u2index =
108             remapVariable(localVariableInfo.u2index);
109     }
110
111
112     // Implementations for LocalVariableTypeInfoVisitor.
113
114     public void visitLocalVariableTypeInfo(Clazz clazz, Method method, CodeAttribute codeAttribute, LocalVariableTypeInfo localVariableTypeInfo)
115     {
116         localVariableTypeInfo.u2index =
117             remapVariable(localVariableTypeInfo.u2index);
118     }
119
120
121     // Implementations for InstructionVisitor.
122
123     public void visitAnyInstruction(Clazz clazz, Method method, CodeAttribute codeAttribute, int offset, Instruction instruction) {}
124
125
126     public void visitVariableInstruction(Clazz clazz, Method method, CodeAttribute codeAttribute, int offset, VariableInstruction variableInstruction)
127     {
128         // Is the new variable index different from the original one?
129 int oldVariableIndex = variableInstruction.variableIndex;
130         int newVariableIndex = remapVariable(oldVariableIndex);
131         if (newVariableIndex != oldVariableIndex)
132         {
133             // Replace the instruction.
134 Instruction replacementInstruction =
135                 new VariableInstruction(variableInstruction.opcode,
136                                         newVariableIndex,
137                                         variableInstruction.constant).shrink();
138
139             codeAttributeEditor.replaceInstruction(offset, replacementInstruction);
140         }
141     }
142
143
144     // Small utility methods.
145
146     /**
147      * Returns the new variable index of the given variable.
148      */
149     private int remapVariable(int variableIndex)
150     {
151         return variableMap[variableIndex];
152     }
153
154
155     /**
156      * Returns the given list of local variables, without the ones that have
157      * been removed.
158      */
159     private int removeEmptyLocalVariables(LocalVariableInfo[] localVariableInfos,
160                                           int localVariableInfoCount)
161     {
162         // Overwrite all empty local variable entries.
163 int newIndex = 0;
164         for (int index = 0; index < localVariableInfoCount; index++)
165         {
166             LocalVariableInfo localVariableInfo = localVariableInfos[index];
167             if (localVariableInfo.u2index >= 0)
168             {
169                 localVariableInfos[newIndex++] = localVariableInfo;
170             }
171         }
172
173         return newIndex;
174     }
175
176
177     /**
178      * Returns the given list of local variable types, without the ones that
179      * have been removed.
180      */
181     private int removeEmptyLocalVariableTypes(LocalVariableTypeInfo[] localVariableTypeInfos,
182                                               int localVariableTypeInfoCount)
183     {
184         // Overwrite all empty local variable type entries.
185 int newIndex = 0;
186         for (int index = 0; index < localVariableTypeInfoCount; index++)
187         {
188             LocalVariableTypeInfo localVariableTypeInfo = localVariableTypeInfos[index];
189             if (localVariableTypeInfo.u2index >= 0)
190             {
191                 localVariableTypeInfos[newIndex++] = localVariableTypeInfo;
192             }
193         }
194
195         return newIndex;
196     }
197 }
198
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