codeattributeeditor.java

ProGuard 是一个免费的 Java类文件的压缩

/*
 * ProGuard -- shrinking, optimization, obfuscation, and preverification
 *             of Java bytecode.
 *
 * Copyright (c) 2002-2007 Eric Lafortune ([e-mail])
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License as published by the Free
 * Software Foundation; either version 2 of the License, or (at your option)
 * any later version.
 *
 * This program is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
 * more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, write to the Free Software Foundation, Inc.,
 * 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 */
package proguard.classfile.editor;

import proguard.classfile.*;
import proguard.classfile.attribute.*;
import proguard.classfile.attribute.preverification.*;
import proguard.classfile.attribute.preverification.visitor.*;
import proguard.classfile.attribute.visitor.*;
import proguard.classfile.instruction.*;
import proguard.classfile.instruction.visitor.InstructionVisitor;
import proguard.classfile.util.SimplifiedVisitor;

/**
 * This AttributeVisitor accumulates specified changes to code, and then applies
 * these accumulated changes to the code attributes that it visits.
 *
 * @author Eric Lafortune
 */
public class CodeAttributeEditor
extends      SimplifiedVisitor
implements   AttributeVisitor,
             InstructionVisitor,
             ExceptionInfoVisitor,
             StackMapFrameVisitor,
             VerificationTypeVisitor,
             LineNumberInfoVisitor,
             LocalVariableInfoVisitor,
             LocalVariableTypeInfoVisitor
{
    private int     codeLength;
    private boolean modified;
    private boolean simple;

    /*private*/public Instruction[]    preInsertions  = new Instruction[ClassConstants.TYPICAL_CODE_LENGTH];
    /*private*/public Instruction[]    replacements   = new Instruction[ClassConstants.TYPICAL_CODE_LENGTH];
    /*private*/public Instruction[]    postInsertions = new Instruction[ClassConstants.TYPICAL_CODE_LENGTH];
    private boolean[]        deleted = new boolean[ClassConstants.TYPICAL_CODE_LENGTH];

    private int[]   instructionOffsetMap = new int[ClassConstants.TYPICAL_CODE_LENGTH];
    private int     newOffset;
    private boolean lengthIncreased;

    private int expectedStackMapFrameOffset;

    private StackSizeUpdater    stackSizeUpdater    = new StackSizeUpdater();
    private VariableSizeUpdater variableSizeUpdater = new VariableSizeUpdater();
    private InstructionWriter   instructionWriter   = new InstructionWriter();


    /**
     * Resets the accumulated code changes.
     * @param codeLength the length of the code that will be edited next.
     */
    public void reset(int codeLength)
    {
        this.codeLength = codeLength;

        // Try to reuse the previous arrays.
        if (preInsertions.length < codeLength)
        {
            preInsertions  = new Instruction[codeLength];
            replacements   = new Instruction[codeLength];
            postInsertions = new Instruction[codeLength];
            deleted        = new boolean[codeLength];
        }
        else
        {
            for (int index = 0; index < codeLength; index++)
            {
                preInsertions[index]  = null;
                replacements[index]   = null;
                postInsertions[index] = null;
                deleted[index]        = false;
            }
        }

        modified = false;
        simple   = true;

    }


    /**
     * Remembers to place the given instruction right before the instruction
     * at the given offset.
     * @param instructionOffset the offset of the instruction.
     * @param instruction       the new instruction.
     */
    public void insertBeforeInstruction(int instructionOffset, Instruction instruction)
    {
        if (instructionOffset < 0 ||
            instructionOffset >= codeLength)
        {
            throw new IllegalArgumentException("Invalid instruction offset ["+instructionOffset+"] in code with length ["+codeLength+"]");
        }

        preInsertions[instructionOffset] = instruction;

        modified = true;
        simple   = false;

    }


    /**
     * Remembers to replace the instruction at the given offset by the given
     * instruction.
     * @param instructionOffset the offset of the instruction to be replaced.
     * @param instruction       the new instruction.
     */
    public void replaceInstruction(int instructionOffset, Instruction instruction)
    {
        if (instructionOffset < 0 ||
            instructionOffset >= codeLength)
        {
            throw new IllegalArgumentException("Invalid instruction offset ["+instructionOffset+"] in code with length ["+codeLength+"]");
        }

        replacements[instructionOffset] = instruction;

        modified = true;
    }


    /**
     * Remembers to place the given instruction right after the instruction
     * at the given offset.
     * @param instructionOffset the offset of the instruction.
     * @param instruction       the new instruction.
     */
    public void insertAfterInstruction(int instructionOffset, Instruction instruction)
    {
        if (instructionOffset < 0 ||
            instructionOffset >= codeLength)
        {
            throw new IllegalArgumentException("Invalid instruction offset ["+instructionOffset+"] in code with length ["+codeLength+"]");
        }

        postInsertions[instructionOffset] = instruction;

        modified = true;
        simple   = false;
    }


    /**
     * Remembers to delete the instruction at the given offset.
     * @param instructionOffset the offset of the instruction to be deleted.
     */
    public void deleteInstruction(int instructionOffset)
    {
        if (instructionOffset < 0 ||
            instructionOffset >= codeLength)
        {
            throw new IllegalArgumentException("Invalid instruction offset ["+instructionOffset+"] in code with length ["+codeLength+"]");
        }

        deleted[instructionOffset] = true;

        modified = true;
        simple   = false;
    }


    /**
     * Remembers not to delete the instruction at the given offset.
     * @param instructionOffset the offset of the instruction not to be deleted.
     */
    public void undeleteInstruction(int instructionOffset)
    {
        if (instructionOffset < 0 ||
            instructionOffset >= codeLength)
        {
            throw new IllegalArgumentException("Invalid instruction offset ["+instructionOffset+"] in code with length ["+codeLength+"]");
        }

        deleted[instructionOffset] = false;
    }


    /**
     * Returns whether the instruction at the given offset has been modified
     * in any way.
     */
    public boolean isModified(int instructionOffset)
    {
        return preInsertions[instructionOffset]  != null ||
               replacements[instructionOffset]   != null ||
               postInsertions[instructionOffset] != null ||
               deleted[instructionOffset];
    }


    // Implementations for AttributeVisitor.

    public void visitAnyAttribute(Clazz clazz, Attribute attribute) {}


    public void visitCodeAttribute(Clazz clazz, Method method, CodeAttribute codeAttribute)
    {
        // Avoid doing any work if nothing is changing anyway.
        if (!modified)
        {
            return;
        }

        // Check if we can perform a faster simple replacement of instructions.
        if (canPerformSimpleReplacements(codeAttribute))
        {
            // Simply overwrite the instructions.
            performSimpleReplacements(codeAttribute);

            // Update the maximum stack size and local variable frame size.
            stackSizeUpdater.visitCodeAttribute(clazz, method, codeAttribute);
            variableSizeUpdater.visitCodeAttribute(clazz, method, codeAttribute);
        }
        else
        {
            // Move and remap the instructions.
            codeAttribute.u4codeLength =
                updateInstructions(clazz, method, codeAttribute);

            // Remap the exception table.
            codeAttribute.exceptionsAccept(clazz, method, this);

            // Remove exceptions with empty code blocks.
            codeAttribute.u2exceptionTableLength =
                removeEmptyExceptions(codeAttribute.exceptionTable,
                                      codeAttribute.u2exceptionTableLength);

            // Update the maximum stack size and local variable frame size.
            stackSizeUpdater.visitCodeAttribute(clazz, method, codeAttribute);
            variableSizeUpdater.visitCodeAttribute(clazz, method, codeAttribute);

            // Remap the line number table and the local variable table.
            codeAttribute.attributesAccept(clazz, method, this);

            // Make sure instructions are widened if necessary.
            instructionWriter.visitCodeAttribute(clazz, method, codeAttribute);
        }
    }


    public void visitStackMapAttribute(Clazz clazz, Method method, CodeAttribute codeAttribute, StackMapAttribute stackMapAttribute)
    {
        // Remap all stack map entries.
        expectedStackMapFrameOffset = -1;
        stackMapAttribute.stackMapFramesAccept(clazz, method, codeAttribute, this);
    }


    public void visitStackMapTableAttribute(Clazz clazz, Method method, CodeAttribute codeAttribute, StackMapTableAttribute stackMapTableAttribute)
    {
        // Remap all stack map table entries.
        expectedStackMapFrameOffset = 0;
        stackMapTableAttribute.stackMapFramesAccept(clazz, method, codeAttribute, this);
    }


    public void visitLineNumberTableAttribute(Clazz clazz, Method method, CodeAttribute codeAttribute, LineNumberTableAttribute lineNumberTableAttribute)
    {
        // Remap all line number table entries.
        lineNumberTableAttribute.lineNumbersAccept(clazz, method, codeAttribute, this);

        // Remove line numbers with empty code blocks.
        lineNumberTableAttribute.u2lineNumberTableLength =
           removeEmptyLineNumbers(lineNumberTableAttribute.lineNumberTable,
                                  lineNumberTableAttribute.u2lineNumberTableLength,
                                  codeAttribute.u4codeLength);
    }


    public void visitLocalVariableTableAttribute(Clazz clazz, Method method, CodeAttribute codeAttribute, LocalVariableTableAttribute localVariableTableAttribute)
    {
        // Remap all local variable table entries.
        localVariableTableAttribute.localVariablesAccept(clazz, method, codeAttribute, this);

        // Remove local variables with empty code blocks.
        localVariableTableAttribute.u2localVariableTableLength =
            removeEmptyLocalVariables(localVariableTableAttribute.localVariableTable,
                                      localVariableTableAttribute.u2localVariableTableLength,
                                      codeAttribute.u2maxLocals);
    }


    public void visitLocalVariableTypeTableAttribute(Clazz clazz, Method method, CodeAttribute codeAttribute, LocalVariableTypeTableAttribute localVariableTypeTableAttribute)
    {
        // Remap all local variable table entries.
        localVariableTypeTableAttribute.localVariablesAccept(clazz, method, codeAttribute, this);