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package com.ibm.wala.demandpa.alg;
import java.util.Collection;
import java.util.HashSet;
import com.ibm.wala.demandpa.alg.statemachine.StateMachine;
import com.ibm.wala.demandpa.alg.statemachine.StateMachineFactory;
import com.ibm.wala.demandpa.alg.statemachine.StatesMergedException;
import com.ibm.wala.demandpa.flowgraph.AssignBarLabel;
import com.ibm.wala.demandpa.flowgraph.AssignGlobalBarLabel;
import com.ibm.wala.demandpa.flowgraph.AssignGlobalLabel;
import com.ibm.wala.demandpa.flowgraph.AssignLabel;
import com.ibm.wala.demandpa.flowgraph.GetFieldBarLabel;
import com.ibm.wala.demandpa.flowgraph.GetFieldLabel;
import com.ibm.wala.demandpa.flowgraph.IFlowLabel;
import com.ibm.wala.demandpa.flowgraph.IFlowLabel.IFlowLabelVisitor;
import com.ibm.wala.demandpa.flowgraph.MatchBarLabel;
import com.ibm.wala.demandpa.flowgraph.MatchLabel;
import com.ibm.wala.demandpa.flowgraph.NewBarLabel;
import com.ibm.wala.demandpa.flowgraph.NewLabel;
import com.ibm.wala.demandpa.flowgraph.ParamBarLabel;
import com.ibm.wala.demandpa.flowgraph.ParamLabel;
import com.ibm.wala.demandpa.flowgraph.PutFieldBarLabel;
import com.ibm.wala.demandpa.flowgraph.PutFieldLabel;
import com.ibm.wala.demandpa.flowgraph.ReturnBarLabel;
import com.ibm.wala.demandpa.flowgraph.ReturnLabel;
import com.ibm.wala.ipa.callgraph.propagation.cfa.CallerSiteContext;
import com.ibm.wala.util.collections.HashSetFactory;
/**
* A state machine for tracking calling context during a points-to query.
* Filters unrealizable paths.
*
*/
public class ContextSensitiveStateMachine implements StateMachine<IFlowLabel> {
private static final boolean DEBUG = false;
private static final boolean DEBUG_RECURSION = false;
/**
* The empty call stack. Note that the empty stack essentially represents all
* possible states.
*/
private final CallStack emptyStack = CallStack.emptyCallStack();
@Override
public CallStack getStartState() {
return emptyStack;
}
private final RecursionHandler recursionHandler;
private class CSLabelVisitor implements IFlowLabelVisitor {
final CallStack prevStack;
State nextState = null;
CSLabelVisitor(CallStack prevStack) {
this.prevStack = prevStack;
}
@Override
public void visitAssign(AssignLabel label, Object dst) {
nextState = prevStack;
}
@Override
public void visitAssignBar(AssignBarLabel label, Object dst) {
nextState = prevStack;
}
@Override
public void visitAssignGlobal(AssignGlobalLabel label, Object dst) {
nextState = emptyStack;
}
@Override
public void visitAssignGlobalBar(AssignGlobalBarLabel label, Object dst) {
nextState = emptyStack;
}
@Override
public void visitGetField(GetFieldLabel label, Object dst) {
nextState = prevStack;
}
@Override
public void visitGetFieldBar(GetFieldBarLabel label, Object dst) {
nextState = prevStack;
}
@Override
public void visitMatch(MatchLabel label, Object dst) {
nextState = emptyStack;
}
@Override
public void visitMatchBar(MatchBarLabel label, Object dst) {
nextState = emptyStack;
}
@Override
public void visitNew(NewLabel label, Object dst) {
nextState = prevStack;
}
@Override
public void visitNewBar(NewBarLabel label, Object dst) {
nextState = prevStack;
}
@Override
public void visitParam(ParamLabel label, Object dst) {
handleMethodExit(label.getCallSite());
}
private void handleMethodExit(CallerSiteContext callSite) {
if (recursionHandler.isRecursive(callSite)) {
nextState = prevStack;
} else if (prevStack.isEmpty()) {
nextState = prevStack;
} else if (prevStack.peek().equals(callSite)) {
nextState = prevStack.pop();
} else {
nextState = ERROR;
}
}
@Override
public void visitParamBar(ParamBarLabel label, Object dst) {
// method entry
handleMethodEntry(label.getCallSite());
}
private void handleMethodEntry(CallerSiteContext callSite) {
if (recursionHandler.isRecursive(callSite)) {
// just ignore it; we don't track recursive calls
nextState = prevStack;
} else if (prevStack.contains(callSite)) {
if (DEBUG_RECURSION) {
System.err.println("FOUND RECURSION");
System.err.println("stack " + prevStack + " contains " + callSite);
}
CallerSiteContext topCallSite = null;
CallStack tmpStack = prevStack;
// mark the appropriate call sites as recursive
// and pop them
Collection<CallerSiteContext> newRecursiveSites = HashSetFactory.make();
do {
topCallSite = tmpStack.peek();
newRecursiveSites.add(topCallSite);
tmpStack = tmpStack.pop();
} while (!topCallSite.equals(callSite) && !tmpStack.isEmpty());
recursionHandler.makeRecursive(newRecursiveSites);
// here we throw the states merged exception to indicate
// that recursion was detected
// ideally, we would update all relevant data structures and continue,
// but it greatly complicates the analysis implementation
throw new StatesMergedException();
} else {
nextState = prevStack.push(callSite);
}
}
@Override
public void visitPutField(PutFieldLabel label, Object dst) {
nextState = prevStack;
}
@Override
public void visitPutFieldBar(PutFieldBarLabel label, Object dst) {
nextState = prevStack;
}
@Override
public void visitReturn(ReturnLabel label, Object dst) {
handleMethodEntry(label.getCallSite());
}
@Override
public void visitReturnBar(ReturnBarLabel label, Object dst) {
handleMethodExit(label.getCallSite());
}
}
/*
* @see com.ibm.wala.demandpa.alg.statemachine.StateMachine#transition(com.ibm.wala.demandpa.alg.statemachine.StateMachine.State, java.lang.Object)
*/
@Override
public State transition(State prevState, IFlowLabel label) throws IllegalArgumentException, IllegalArgumentException {
if (prevState == null) {
throw new IllegalArgumentException("prevState == null");
}
if (!(prevState instanceof CallStack)) {
throw new IllegalArgumentException("not ( prevState instanceof com.ibm.wala.demandpa.alg.CallStack ) ");
}
CallStack prevStack = (CallStack) prevState;
if (!prevStack.isEmpty() && recursionHandler.isRecursive(prevStack.peek())) {
// I don't think this is possible anymore
assert false;
// just pop off the call site
return transition(prevStack.pop(), label);
}
CSLabelVisitor v = new CSLabelVisitor(prevStack);
label.visit(v, null);
if (DEBUG) {
if (prevStack != v.nextState && v.nextState != ERROR) {
System.err.println("prev stack " + prevStack);
System.err.println("label " + label);
System.err.println("recursive call sites " + recursionHandler);
System.err.println("next stack " + v.nextState);
}
}
return v.nextState;
}
private ContextSensitiveStateMachine(RecursionHandler recursionHandler) {
this.recursionHandler = recursionHandler;
}
public static class Factory implements StateMachineFactory<IFlowLabel> {
private final RecursionHandler prototype;
public Factory(RecursionHandler prototype) {
this.prototype = prototype;
}
public Factory() {
this(new BasicRecursionHandler());
}
@Override
public StateMachine<IFlowLabel> make() {
return new ContextSensitiveStateMachine(prototype.makeNew());
}
}
public static interface RecursionHandler {
public boolean isRecursive(CallerSiteContext callSite);
public void makeRecursive(Collection<CallerSiteContext> callSites);
/**
* in lieu of creating factories
*/
public RecursionHandler makeNew();
}
/**
* handles method recursion by only collapsing cycles of recursive
* calls observed during analysis
*/
public static class BasicRecursionHandler implements RecursionHandler {
private final HashSet<CallerSiteContext> recursiveCallSites = HashSetFactory.make();
@Override
public boolean isRecursive(CallerSiteContext callSite) {
return recursiveCallSites.contains(callSite);
}
@Override
public void makeRecursive(Collection<CallerSiteContext> callSites) {
recursiveCallSites.addAll(callSites);
}
@Override
public RecursionHandler makeNew() {
return new BasicRecursionHandler();
}
}
}