codeattributecomposer.java

ProGuard 是一个免费的 Java类文件的压缩

        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);

        // Remove local variables with empty code blocks.
        localVariableTypeTableAttribute.u2localVariableTypeTableLength =
            removeEmptyLocalVariableTypes(localVariableTypeTableAttribute.localVariableTypeTable,
                                          localVariableTypeTableAttribute.u2localVariableTypeTableLength,
                                          codeAttribute.u2maxLocals);
    }


    // Implementations for InstructionVisitor.

    public void visitAnyInstruction(Clazz clazz, Method method, CodeAttribute codeAttribute, int offset, Instruction instruction) {}


    public void visitBranchInstruction(Clazz clazz, Method method, CodeAttribute codeAttribute, int offset, BranchInstruction branchInstruction)
    {
        // Adjust the branch offset.
        branchInstruction.branchOffset = remapBranchOffset(offset,
                                                           branchInstruction.branchOffset);
    }


    public void visitTableSwitchInstruction(Clazz clazz, Method method, CodeAttribute codeAttribute, int offset, TableSwitchInstruction tableSwitchInstruction)
    {
        // Adjust the default jump offset.
        tableSwitchInstruction.defaultOffset = remapBranchOffset(offset,
                                                                 tableSwitchInstruction.defaultOffset);

        // Adjust the jump offsets.
        remapJumpOffsets(offset,
                         tableSwitchInstruction.jumpOffsets,
                         tableSwitchInstruction.highCase -
                         tableSwitchInstruction.lowCase + 1);
    }


    public void visitLookUpSwitchInstruction(Clazz clazz, Method method, CodeAttribute codeAttribute, int offset, LookUpSwitchInstruction lookUpSwitchInstruction)
    {
        // Adjust the default jump offset.
        lookUpSwitchInstruction.defaultOffset = remapBranchOffset(offset,
                                                                  lookUpSwitchInstruction.defaultOffset);

        // Adjust the jump offsets.
        remapJumpOffsets(offset,
                         lookUpSwitchInstruction.jumpOffsets,
                         lookUpSwitchInstruction.jumpOffsetCount);
    }


    // Implementations for ExceptionInfoVisitor.

    public void visitExceptionInfo(Clazz clazz, Method method, CodeAttribute codeAttribute, ExceptionInfo exceptionInfo)
    {
        // Remap the code offsets. Note that the instruction offset map also has
        // an entry for the first offset after the code, for u2endPC.
        exceptionInfo.u2startPC   = remapInstructionOffset(exceptionInfo.u2startPC);
        exceptionInfo.u2endPC     = remapInstructionOffset(exceptionInfo.u2endPC);
        exceptionInfo.u2handlerPC = remapInstructionOffset(exceptionInfo.u2handlerPC);
    }


    // Implementations for StackMapFrameVisitor.

    public void visitAnyStackMapFrame(Clazz clazz, Method method, CodeAttribute codeAttribute, int offset, StackMapFrame stackMapFrame)
    {
        // Remap the stack map frame offset.
        int stackMapFrameOffset = remapInstructionOffset(offset);

        int offsetDelta = stackMapFrameOffset;

        // Compute the offset delta if the frame is part of a stack map frame
        // table (for JDK 6.0) instead of a stack map (for Java Micro Edition).
        if (expectedStackMapFrameOffset >= 0)
        {
            offsetDelta -= expectedStackMapFrameOffset;

            expectedStackMapFrameOffset = stackMapFrameOffset + 1;
        }

        stackMapFrame.u2offsetDelta = offsetDelta;
    }


    public void visitSameOneFrame(Clazz clazz, Method method, CodeAttribute codeAttribute, int offset, SameOneFrame sameOneFrame)
    {
        // Remap the stack map frame offset.
        visitAnyStackMapFrame(clazz, method, codeAttribute, offset, sameOneFrame);

        // Remap the verification type offset.
        sameOneFrame.stackItemAccept(clazz, method, codeAttribute, offset, this);
    }


    public void visitMoreZeroFrame(Clazz clazz, Method method, CodeAttribute codeAttribute, int offset, MoreZeroFrame moreZeroFrame)
    {
        // Remap the stack map frame offset.
        visitAnyStackMapFrame(clazz, method, codeAttribute, offset, moreZeroFrame);

        // Remap the verification type offsets.
        moreZeroFrame.additionalVariablesAccept(clazz, method, codeAttribute, offset, this);
    }


    public void visitFullFrame(Clazz clazz, Method method, CodeAttribute codeAttribute, int offset, FullFrame fullFrame)
    {
        // Remap the stack map frame offset.
        visitAnyStackMapFrame(clazz, method, codeAttribute, offset, fullFrame);

        // Remap the verification type offsets.
        fullFrame.variablesAccept(clazz, method, codeAttribute, offset, this);
        fullFrame.stackAccept(clazz, method, codeAttribute, offset, this);
    }


    // Implementations for VerificationTypeVisitor.

    public void visitAnyVerificationType(Clazz clazz, Method method, CodeAttribute codeAttribute, int offset, VerificationType verificationType) {}


    public void visitUninitializedType(Clazz clazz, Method method, CodeAttribute codeAttribute, int offset, UninitializedType uninitializedType)
    {
        // Remap the offset of the 'new' instruction.
        uninitializedType.u2newInstructionOffset = remapInstructionOffset(uninitializedType.u2newInstructionOffset);
    }


    // Implementations for LineNumberInfoVisitor.

    public void visitLineNumberInfo(Clazz clazz, Method method, CodeAttribute codeAttribute, LineNumberInfo lineNumberInfo)
    {
        // Remap the code offset.
        lineNumberInfo.u2startPC = remapInstructionOffset(lineNumberInfo.u2startPC);
    }


    // Implementations for LocalVariableInfoVisitor.

    public void visitLocalVariableInfo(Clazz clazz, Method method, CodeAttribute codeAttribute, LocalVariableInfo localVariableInfo)
    {
        // Remap the code offset and length.
        // TODO: The local variable frame might not be strictly preserved.
        int startPC = remapInstructionOffset(localVariableInfo.u2startPC);
        int endPC   = remapInstructionOffset(localVariableInfo.u2startPC + localVariableInfo.u2length);

        localVariableInfo.u2startPC = startPC;
        localVariableInfo.u2length  = endPC - startPC;
    }

    // Implementations for LocalVariableTypeInfoVisitor.

    public void visitLocalVariableTypeInfo(Clazz clazz, Method method, CodeAttribute codeAttribute, LocalVariableTypeInfo localVariableTypeInfo)
    {
        // Remap the code offset and length.
        // TODO: The local variable frame might not be strictly preserved.
        int startPC = remapInstructionOffset(localVariableTypeInfo.u2startPC);
        int endPC   = remapInstructionOffset(localVariableTypeInfo.u2startPC + localVariableTypeInfo.u2length);

        localVariableTypeInfo.u2length  = startPC;
        localVariableTypeInfo.u2startPC = endPC - startPC;
    }


    // Small utility methods.

    /**
     * Adjusts the given jump offsets for the instruction at the given offset.
     */
    private void remapJumpOffsets(int offset, int[] jumpOffsets, int length)
    {
        for (int index = 0; index < length; index++)
        {
            jumpOffsets[index] = remapBranchOffset(offset, jumpOffsets[index]);
        }
    }


    /**
     * Computes the new branch offset for the instruction at the given new offset
     * with the given old branch offset.
     */
    private int remapBranchOffset(int newInstructionOffset, int branchOffset)
    {
        if (newInstructionOffset < 0 ||
            newInstructionOffset > codeLength)
        {
            throw new IllegalArgumentException("Invalid instruction offset ["+newInstructionOffset +"] in code with length ["+codeLength+"]");
        }

        int oldInstructionOffset = oldInstructionOffsets[newInstructionOffset];

        return remapInstructionOffset(oldInstructionOffset + branchOffset) -
               remapInstructionOffset(oldInstructionOffset);
    }


    /**
     * Computes the new instruction offset for the instruction at the given old
     * offset.
     */
    private int remapInstructionOffset(int oldInstructionOffset)
    {
        if (oldInstructionOffset < 0 ||
            oldInstructionOffset > codeFragmentLengths[level])
        {
            throw new IllegalArgumentException("Invalid instruction offset ["+oldInstructionOffset +"] in code fragment with length ["+codeFragmentLengths[level]+"]");
        }

        return instructionOffsetMap[level][oldInstructionOffset];
    }


    /**
     * Returns the given list of exceptions, without the ones that have empty
     * code blocks.
     */
    private int removeEmptyExceptions(ExceptionInfo[] exceptionInfos,
                                      int             exceptionInfoCount)
    {
        // Overwrite all empty exceptions.
        int newIndex = 0;
        for (int index = 0; index < exceptionInfoCount; index++)
        {
            ExceptionInfo exceptionInfo = exceptionInfos[index];
            if (exceptionInfo.u2startPC < exceptionInfo.u2endPC)
            {
                exceptionInfos[newIndex++] = exceptionInfo;
            }
        }

        // Clear the unused array entries.
        for (int index = newIndex; index < exceptionInfoCount; index++)
        {
            exceptionInfos[index] = null;
        }

        return newIndex;
    }


    /**
     * Returns the given list of line numbers, without the ones that have empty
     * code blocks or that exceed the code size.
     */
    private int removeEmptyLineNumbers(LineNumberInfo[] lineNumberInfos,
                                       int              lineNumberInfoCount,
                                       int              codeLength)
    {
        // Overwrite all empty line number entries.
        int newIndex = 0;
        for (int index = 0; index < lineNumberInfoCount; index++)
        {
            LineNumberInfo lineNumberInfo = lineNumberInfos[index];
            int startPC = lineNumberInfo.u2startPC;
            if (startPC < codeLength &&
                (index == 0 || startPC > lineNumberInfos[index-1].u2startPC))
            {
                lineNumberInfos[newIndex++] = lineNumberInfo;
            }
        }

        // Clear the unused array entries.
        for (int index = newIndex; index < lineNumberInfoCount; index++)
        {
            lineNumberInfos[index] = null;
        }

        return newIndex;
    }


    /**
     * Returns the given list of local variables, without the ones that have empty
     * code blocks or that exceed the actual number of local variables.
     */
    private int removeEmptyLocalVariables(LocalVariableInfo[] localVariableInfos,
                                          int                 localVariableInfoCount,
                                          int                 maxLocals)
    {
        // Overwrite all empty local variable entries.
        int newIndex = 0;
        for (int index = 0; index < localVariableInfoCount; index++)
        {
            LocalVariableInfo localVariableInfo = localVariableInfos[index];
            if (localVariableInfo.u2length > 0 &&
                localVariableInfo.u2index < maxLocals)
            {
                localVariableInfos[newIndex++] = localVariableInfo;
            }
        }

        // Clear the unused array entries.
        for (int index = newIndex; index < localVariableInfoCount; index++)
        {
            localVariableInfos[index] = null;
        }

        return newIndex;
    }


    /**
     * Returns the given list of local variable types, without the ones that
     * have empty code blocks or that exceed the actual number of local variables.
     */
    private int removeEmptyLocalVariableTypes(LocalVariableTypeInfo[] localVariableTypeInfos,
                                              int                     localVariableTypeInfoCount,
                                              int                     maxLocals)
    {
        // Overwrite all empty local variable type entries.
        int newIndex = 0;
        for (int index = 0; index < localVariableTypeInfoCount; index++)
        {
            LocalVariableTypeInfo localVariableTypeInfo = localVariableTypeInfos[index];
            if (localVariableTypeInfo.u2length > 0 &&
                localVariableTypeInfo.u2index < maxLocals)
            {
                localVariableTypeInfos[newIndex++] = localVariableTypeInfo;
            }
        }

        // Clear the unused array entries.
        for (int index = newIndex; index < localVariableTypeInfoCount; index++)
        {
            localVariableTypeInfos[index] = null;
        }

        return newIndex;
    }


    public static void main(String[] args)
    {
        CodeAttributeComposer composer = new CodeAttributeComposer();

        composer.beginCodeFragment(10);
        composer.appendInstruction(0, new SimpleInstruction(InstructionConstants.OP_ICONST_0));
        composer.appendInstruction(1, new VariableInstruction(InstructionConstants.OP_ISTORE, 0));
        composer.appendInstruction(2, new BranchInstruction(InstructionConstants.OP_GOTO, 1));

        composer.beginCodeFragment(10);
        composer.appendInstruction(0, new VariableInstruction(InstructionConstants.OP_IINC, 0, 1));
        composer.appendInstruction(1, new VariableInstruction(InstructionConstants.OP_ILOAD, 0));
        composer.appendInstruction(2, new SimpleInstruction(InstructionConstants.OP_ICONST_5));
        composer.appendInstruction(3, new BranchInstruction(InstructionConstants.OP_IFICMPLT, -3));
        composer.endCodeFragment();

        composer.appendInstruction(3, new SimpleInstruction(InstructionConstants.OP_RETURN));
        composer.endCodeFragment();
    }
}