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ProGuard is a free shrinker, optimizer, obfuscator, and preverifier for Java bytecode
/*
* ProGuard -- shrinking, optimization, obfuscation, and preverification
* of Java bytecode.
*
* Copyright (c) 2002-2021 Guardsquare NV
*
* 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.optimize.peephole;
import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;
import proguard.classfile.*;
import proguard.classfile.attribute.*;
import proguard.classfile.attribute.visitor.AttributeVisitor;
import proguard.classfile.constant.*;
import proguard.classfile.constant.visitor.ConstantVisitor;
import proguard.classfile.editor.CodeAttributeEditor;
import proguard.classfile.instruction.*;
import proguard.classfile.instruction.visitor.InstructionVisitor;
import proguard.classfile.visitor.ClassVisitor;
import proguard.optimize.info.WrapperClassMarker;
/**
* This AttributeVisitor simplifies the use of retargeted wrapper classes in
* the code attributes that it visits. More specifically, it replaces
* "new Wrapper(targetClass)" by "targetClass", and
* "wrapper.field" by "wrapper".
* You still need to retarget all class references, replacing references to
* the wrapper class by references to the target class.
*
* @see WrapperClassMarker
* @see ClassMerger
* @see RetargetedClassFilter
* @see TargetClassChanger
* @author Eric Lafortune
*/
public class WrapperClassUseSimplifier
implements AttributeVisitor,
InstructionVisitor,
ConstantVisitor,
ClassVisitor
{
private static final Logger logger = LogManager.getLogger(WrapperClassUseSimplifier.class);
private final InstructionVisitor extraInstructionVisitor;
private final CodeAttributeEditor codeAttributeEditor = new CodeAttributeEditor(true, true);
// Fields acting as parameters and return values for the visitor methods.
private Clazz wrappedClass;
private boolean isDupedOnStack;
private Instruction storeInstruction;
/**
* Creates a new WrapperClassUseSimplifier.
*/
public WrapperClassUseSimplifier()
{
this(null);
}
/**
* Creates a new WrapperClassUseSimplifier.
* @param extraInstructionVisitor an optional extra visitor for all
* simplified instructions.
*/
public WrapperClassUseSimplifier(InstructionVisitor extraInstructionVisitor)
{
this.extraInstructionVisitor = extraInstructionVisitor;
}
// Implementations for AttributeVisitor.
public void visitAnyAttribute(Clazz clazz, Attribute attribute) {}
public void visitCodeAttribute(Clazz clazz, Method method, CodeAttribute codeAttribute)
{
logger.debug("WrapperClassUseSimplifier: {}.{}{}",
clazz.getName(),
method.getName(clazz),
method.getDescriptor(clazz));
int codeLength = codeAttribute.u4codeLength;
// Reset the code changes.
codeAttributeEditor.reset(codeLength);
// Edit the instructions.
codeAttribute.instructionsAccept(clazz, method, this);
// Apply all accumulated changes to the code.
codeAttributeEditor.visitCodeAttribute(clazz, method, codeAttribute);
}
// Implementations for InstructionVisitor.
public void visitAnyInstruction(Clazz clazz, Method method, CodeAttribute codeAttribute, int offset, Instruction instruction) {}
public void visitConstantInstruction(Clazz clazz, Method method, CodeAttribute codeAttribute, int offset, ConstantInstruction constantInstruction)
{
switch (constantInstruction.opcode)
{
case Instruction.OP_NEW:
{
// Is it instantiating a wrapper class?
if (isReferencingWrapperClass(clazz, constantInstruction.constantIndex))
{
// We at least need to handle any of these sequences:
// new -> (nothing)
// new / dup -> (nothing)
// new / astore / aload -> (nothing)
// new / dup / astore -> (nothing)
// Replace the new instance by a dummy null.
codeAttributeEditor.deleteInstruction(offset);
// Look at the next instruction.
offset += constantInstruction.length(offset);
Instruction nextInstruction = InstructionFactory.create(codeAttribute.code, offset);
// Is the next instruction a (typical) dup instruction?
isDupedOnStack = nextInstruction.opcode == Instruction.OP_DUP;
if (isDupedOnStack)
{
// Delete the duplicate.
codeAttributeEditor.deleteInstruction(offset);
// Look at the next instruction.
offset += nextInstruction.length(offset);
nextInstruction = InstructionFactory.create(codeAttribute.code, offset);
}
// Is the next instruction a (less common) store instruction?
if (nextInstruction.canonicalOpcode() == Instruction.OP_ASTORE)
{
// Delete the store.
codeAttributeEditor.deleteInstruction(offset);
// Remember the store instruction, so we can use it to
// store the wrapped class later on.
storeInstruction = nextInstruction;
// Look at the next instruction.
offset += nextInstruction.length(offset);
nextInstruction = InstructionFactory.create(codeAttribute.code, offset);
// Is the next instruction the corresponding load
// instruction?
if (nextInstruction.canonicalOpcode() == Instruction.OP_ALOAD &&
((VariableInstruction)storeInstruction).variableIndex ==
((VariableInstruction)nextInstruction ).variableIndex)
{
// Delete the load.
codeAttributeEditor.deleteInstruction(offset);
// Remember that the original code had a duplicate
// of the wrapper on the stack.
isDupedOnStack = true;
}
}
else
{
storeInstruction = null;
}
if (extraInstructionVisitor != null)
{
extraInstructionVisitor.visitConstantInstruction(clazz, method, codeAttribute, offset, constantInstruction);
}
}
break;
}
case Instruction.OP_INVOKESPECIAL:
{
// Is it initializing a wrapper class?
if (isReferencingWrapperClass(clazz, constantInstruction.constantIndex))
{
// Replace the initializer invocation, popping or storing
// the wrapped instance from the stack.
// TODO: May still fail with nested initializers for different wrapper classes.
// Do we have a store instruction?
if (storeInstruction != null)
{
// The wrapper was stored beforehand. Store the wrapped
// instance now.
// wrapper.(target) -> astore
codeAttributeEditor.replaceInstruction(offset, storeInstruction);
}
else if (isDupedOnStack)
{
// The wrapper was originally duplicated on the stack.
// Delete the initializer invocation, leaving just the
// wrapped instance on the stack:
// wrapper.(target) -> (target)
// A subsequent astore/putfield/... should consume it.
codeAttributeEditor.deleteInstruction(offset);
}
else
{
// The wrapper wasn't duplicated on the stack or
// stored in a variable. Just pop the wrapped instance.
// wrapper.(target) -> pop
codeAttributeEditor.replaceInstruction(offset, new SimpleInstruction(Instruction.OP_POP));
}
}
break;
}
case Instruction.OP_GETFIELD:
{
// Is it retrieving the field of the wrapper class?
if (isReferencingWrapperClass(clazz, constantInstruction.constantIndex))
{
// Delete the retrieval:
// wrapper.field -> wrapper
codeAttributeEditor.deleteInstruction(offset);
}
break;
}
}
}
// Implementations for ConstantVisitor.
public void visitAnyConstant(Clazz clazz, Constant constant) {}
public void visitFieldrefConstant(Clazz clazz, FieldrefConstant fieldrefConstant)
{
// Is the constant retrieving from a wrapper class?
fieldrefConstant.referencedClassAccept(this);
}
public void visitMethodrefConstant(Clazz clazz, MethodrefConstant methodrefConstant)
{
if (methodrefConstant.getName(clazz).equals(ClassConstants.METHOD_NAME_INIT))
{
// Is the constant referring to a wrapper class?
methodrefConstant.referencedClassAccept(this);
}
}
public void visitClassConstant(Clazz clazz, ClassConstant classConstant)
{
// Is the constant referring to a wrapper class?
classConstant.referencedClassAccept(this);
}
// Implementations for ClassVisitor.
@Override
public void visitAnyClass(Clazz clazz) { }
@Override
public void visitProgramClass(ProgramClass programClass)
{
wrappedClass = ClassMerger.getTargetClass(programClass);
}
// Small utility methods.
/**
* Returns whether the constant at the given offset is referencing a
* wrapper class (different from the given class) that is being retargeted.
*/
private boolean isReferencingWrapperClass(Clazz clazz, int constantIndex)
{
wrappedClass = null;
clazz.constantPoolEntryAccept(constantIndex, this);
return wrappedClass != null;
}
}
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