/***
* ASM Guide
* Copyright (c) 2007 Eric Bruneton
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. Neither the name of the copyright holders nor the names of its
* contributors may be used to endorse or promote products derived from
* this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
* THE POSSIBILITY OF SUCH DAMAGE.
*/
package ch7.sec2;
import static org.objectweb.asm.Opcodes.ARRAYLENGTH;
import static org.objectweb.asm.Opcodes.GETFIELD;
import static org.objectweb.asm.Opcodes.INVOKEINTERFACE;
import static org.objectweb.asm.Opcodes.INVOKESPECIAL;
import static org.objectweb.asm.Opcodes.INVOKEVIRTUAL;
import static org.objectweb.asm.Opcodes.MONITORENTER;
import static org.objectweb.asm.Opcodes.MONITOREXIT;
import static org.objectweb.asm.Opcodes.PUTFIELD;
import static org.objectweb.asm.tree.analysis.BasicValue.REFERENCE_VALUE;
import java.util.ArrayList;
import java.util.List;
import org.objectweb.asm.Type;
import org.objectweb.asm.tree.AbstractInsnNode;
import org.objectweb.asm.tree.MethodInsnNode;
import org.objectweb.asm.tree.MethodNode;
import org.objectweb.asm.tree.analysis.Analyzer;
import org.objectweb.asm.tree.analysis.AnalyzerException;
import org.objectweb.asm.tree.analysis.BasicInterpreter;
import org.objectweb.asm.tree.analysis.BasicValue;
import org.objectweb.asm.tree.analysis.Frame;
import org.objectweb.asm.tree.analysis.Value;
/**
* ASM Guide example class.
*
* @author Eric Bruneton
*/
public class NullDereferenceAnalyzer {
public List<AbstractInsnNode> findNullDereferences(String owner,
MethodNode mn) throws AnalyzerException {
List<AbstractInsnNode> result = new ArrayList<AbstractInsnNode>();
Analyzer a = new Analyzer(new IsNullInterpreter());
a.analyze(owner, mn);
Frame[] frames = a.getFrames();
AbstractInsnNode[] insns = mn.instructions.toArray();
for (int i = 0; i < insns.length; ++i) {
AbstractInsnNode insn = insns[i];
if (frames[i] != null) {
Value v = getTarget(insn, frames[i]);
if (v == IsNullInterpreter.NULL
|| v == IsNullInterpreter.MAYBENULL) {
result.add(insn);
}
}
}
return result;
}
private static Value getTarget(AbstractInsnNode insn, Frame f) {
switch (insn.getOpcode()) {
case GETFIELD:
case ARRAYLENGTH:
case MONITORENTER:
case MONITOREXIT:
return getStackValue(f, 0);
case PUTFIELD:
return getStackValue(f, 1);
case INVOKEVIRTUAL:
case INVOKESPECIAL:
case INVOKEINTERFACE:
String desc = ((MethodInsnNode) insn).desc;
return getStackValue(f, Type.getArgumentTypes(desc).length);
}
return null;
}
private static Value getStackValue(Frame f, int index) {
int top = f.getStackSize() - 1;
return index <= top ? f.getStack(top - index) : null;
}
}
class IsNullInterpreter extends BasicInterpreter {
public final static BasicValue NULL = new BasicValue(null);
public final static BasicValue MAYBENULL = new BasicValue(null);
@Override
public Value newOperation(AbstractInsnNode insn) {
if (insn.getOpcode() == ACONST_NULL) {
return NULL;
}
return super.newOperation(insn);
}
@Override
public Value merge(Value v, Value w) {
if (isRef(v) && isRef(w) && v != w) {
return MAYBENULL;
}
return super.merge(v, w);
}
private boolean isRef(Value v) {
return v == REFERENCE_VALUE || v == NULL || v == MAYBENULL;
}
}