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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;
import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;
import proguard.classfile.*;
import proguard.classfile.attribute.CodeAttribute;
import proguard.classfile.constant.*;
import proguard.classfile.constant.visitor.ConstantVisitor;
import proguard.classfile.editor.*;
import proguard.classfile.instruction.*;
import proguard.classfile.instruction.visitor.InstructionVisitor;
import proguard.classfile.visitor.ClassVisitor;
import proguard.util.ProcessingFlags;
/**
* This InstructionVisitor generalizes the classes referenced by the
* field/method invocation instructions that it visits.
*
* For example, it replaces invocations
* StringBuilder#toString() by Object#toString(),
* Integer#intValue() by Number#intValue(),
* Exception#printStackTrace() by Throwable#printStackTrace().
*
* @author Eric Lafortune
*/
public class MemberReferenceGeneralizer
implements InstructionVisitor,
ConstantVisitor,
ClassVisitor
{
private static final Logger logger = LogManager.getLogger(MemberReferenceGeneralizer.class);
private final boolean fieldGeneralizationClass;
private final boolean methodGeneralizationClass;
private final CodeAttributeEditor codeAttributeEditor;
private final InstructionVisitor extraFieldInstructionVisitor;
private final InstructionVisitor extraMethodInstructionVisitor;
// Fields acting as parameters and return values for the visitor methods.
private int invocationOffset;
private byte invocationOpcode;
private String memberName;
private String memberType;
private Clazz generalizedClass;
private Member generalizedMember;
/**
* Creates a new ReferenceGeneralizer.
* @param fieldGeneralizationClass specifies whether field classes should
* be generalized.
* @param methodGeneralizationClass specifies whether method classes
* should be generalized.
* @param codeAttributeEditor a code editor that can be used to
* accumulate changes to the code.
*/
public MemberReferenceGeneralizer(boolean fieldGeneralizationClass,
boolean methodGeneralizationClass,
CodeAttributeEditor codeAttributeEditor)
{
this(fieldGeneralizationClass,
methodGeneralizationClass,
codeAttributeEditor,
null,
null);
}
/**
* Creates a new ReferenceGeneralizer.
* @param fieldGeneralizationClass specifies whether field classes
* should be generalized.
* @param methodGeneralizationClass specifies whether method classes
* should be generalized.
* @param codeAttributeEditor a code editor that can be used to
* accumulate changes to the code.
* @param extraFieldInstructionVisitor an extra visitor for all field
* access instructions whose
* referenced classes have been
* generalized.
* @param extraMethodInstructionVisitor an extra visitor for all method
* invocations instructions whose
* referenced classes have been
* generalized.
*/
public MemberReferenceGeneralizer(boolean fieldGeneralizationClass,
boolean methodGeneralizationClass,
CodeAttributeEditor codeAttributeEditor,
InstructionVisitor extraFieldInstructionVisitor,
InstructionVisitor extraMethodInstructionVisitor)
{
this.fieldGeneralizationClass = fieldGeneralizationClass;
this.methodGeneralizationClass = methodGeneralizationClass;
this.codeAttributeEditor = codeAttributeEditor;
this.extraFieldInstructionVisitor = extraFieldInstructionVisitor;
this.extraMethodInstructionVisitor = extraMethodInstructionVisitor;
}
// Implementations for InstructionVisitor.
@Override
public void visitAnyInstruction(Clazz clazz, Method method, CodeAttribute codeAttribute, int offset, Instruction instruction) {}
@Override
public void visitConstantInstruction(Clazz clazz, Method method, CodeAttribute codeAttribute, int offset, ConstantInstruction constantInstruction)
{
// Is it a virtual method invocation?
byte opcode = constantInstruction.opcode;
switch (opcode)
{
case Instruction.OP_GETFIELD:
case Instruction.OP_PUTFIELD:
{
if (fieldGeneralizationClass &&
!codeAttributeEditor.isModified(offset))
{
// Try to generalize the field reference.
invocationOffset = offset;
invocationOpcode = opcode;
clazz.constantPoolEntryAccept(constantInstruction.constantIndex, this);
// Did we find a class with the class member?
if (generalizedClass != null &&
extraFieldInstructionVisitor != null)
{
extraFieldInstructionVisitor.visitConstantInstruction(clazz,
method,
codeAttribute,
offset,
constantInstruction);
}
}
break;
}
case Instruction.OP_INVOKEVIRTUAL:
{
if (methodGeneralizationClass &&
!codeAttributeEditor.isModified(offset))
{
// Try to generalize the method invocation.
invocationOffset = offset;
invocationOpcode = opcode;
clazz.constantPoolEntryAccept(constantInstruction.constantIndex, this);
// Did we find a class with the class member?
if (generalizedClass != null &&
extraMethodInstructionVisitor != null)
{
extraMethodInstructionVisitor.visitConstantInstruction(clazz,
method,
codeAttribute,
offset,
constantInstruction);
}
}
break;
}
}
}
// Implementations for ConstantVisitor.
@Override
public void visitAnyRefConstant(Clazz clazz, RefConstant refConstant)
{
// Try to find the class member in the super class (or higher).
memberName = refConstant.getName(clazz);
memberType = refConstant.getType(clazz);
generalizedClass = null;
generalizedMember = null;
Member referencedMember = refConstant instanceof FieldrefConstant ?
((FieldrefConstant)refConstant).referencedField : ((AnyMethodrefConstant)refConstant).referencedMethod;
// DGD-486: Only generalize members which are always available. Partial replacement of a class that is not
// available on all platforms may result in a VerifyError at runtime.
if (referencedMember != null &&
(referencedMember.getProcessingFlags() & ProcessingFlags.IS_CLASS_AVAILABLE) != 0)
{
clazz.constantPoolEntryAccept(refConstant.u2classIndex, this);
// Did we find a class with the class member?
if (generalizedClass != null &&
// only update the RefConstant if the generalized class is different
// from the existing one. This can happen for fields as we need to first
// look in the current class. Use the actual class name to compare as the
// ClassReferenceInitializer might have found the proper class in the
// hierarchy.
!generalizedClass.getName().equals(refConstant.getClassName(clazz)))
{
logger.debug("ReferenceGeneralizer: [{}] invocation [{}.{}{}] -> [{}. ...]",
clazz.getName(),
refConstant.getClassName(clazz),
memberName,
memberType,
generalizedClass.getName()
);
int refConstantIndex;
// Prevent concurrent modification of the constant pool from multiple threads.
synchronized (clazz)
{
ConstantPoolEditor constantPoolEditor =
new ConstantPoolEditor((ProgramClass)clazz);
// Replace the invocation instruction.
int generalizedClassConstantIndex =
constantPoolEditor.addClassConstant(generalizedClass);
refConstantIndex =
invocationOpcode != Instruction.OP_INVOKEVIRTUAL ?
constantPoolEditor.addFieldrefConstant(generalizedClassConstantIndex,
memberName,
memberType,
generalizedClass,
(Field)generalizedMember) :
constantPoolEditor.addMethodrefConstant(generalizedClassConstantIndex,
memberName,
memberType,
generalizedClass,
(Method)generalizedMember);
}
ConstantInstruction replacementInstruction =
new ConstantInstruction(invocationOpcode, refConstantIndex);
codeAttributeEditor.replaceInstruction(invocationOffset,
replacementInstruction);
}
else
{
generalizedClass = null;
}
}
}
@Override
public void visitClassConstant(Clazz clazz, ClassConstant classConstant)
{
// Try to find the method in the super class (or higher).
classConstant.referencedClassAccept(this);
}
// Implementations for ClassVisitor.
@Override
public void visitAnyClass(Clazz clazz)
{
if (invocationOpcode == Instruction.OP_INVOKEVIRTUAL)
{
// Do we have a super class?
Clazz superClass = clazz.getSuperClass();
if (superClass != null)
{
// First look higher up in the hierarchy.
superClass.accept(this);
// Otherwise, look in the super class itself.
// Only consider public classes and methods, to avoid any
// access problems.
if (generalizedClass == null &&
(superClass.getAccessFlags() & AccessConstants.PUBLIC) != 0)
{
Method method = superClass.findMethod(memberName, memberType);
if (method != null &&
(method.getAccessFlags() & AccessConstants.PUBLIC) != 0 &&
(method.getProcessingFlags() & ProcessingFlags.IS_CLASS_AVAILABLE) != 0)
{
// Remember the generalized class and class member.
generalizedClass = superClass;
generalizedMember = method;
}
}
}
}
else
{
// First look for the field in the class itself.
Field field = clazz.findField(memberName, memberType);
if (field != null &&
(field.getProcessingFlags() & ProcessingFlags.IS_CLASS_AVAILABLE) != 0)
{
// Remember the generalized class and class member.
generalizedClass = clazz;
generalizedMember = field;
}
else
{
// Do we have a super class?
Clazz superClass = clazz.getSuperClass();
if (superClass != null)
{
// Look higher up in the hierarchy.
superClass.accept(this);
}
}
}
}
}
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