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      1 /*
      2  * ProGuard -- shrinking, optimization, obfuscation, and preverification
      3  *             of Java bytecode.
      4  *
      5  * Copyright (c) 2002-2009 Eric Lafortune (eric (at) 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 final 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