/*
* Copyright 2000-2004 The Apache Software Foundation
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
*/
package org.apache.bcel.verifier.structurals;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.Hashtable;
import org.apache.bcel.generic.ATHROW;
import org.apache.bcel.generic.BranchInstruction;
import org.apache.bcel.generic.GotoInstruction;
import org.apache.bcel.generic.Instruction;
import org.apache.bcel.generic.InstructionHandle;
import org.apache.bcel.generic.JsrInstruction;
import org.apache.bcel.generic.MethodGen;
import org.apache.bcel.generic.RET;
import org.apache.bcel.generic.ReturnInstruction;
import org.apache.bcel.generic.Select;
import org.apache.bcel.verifier.exc.AssertionViolatedException;
import org.apache.bcel.verifier.exc.StructuralCodeConstraintException;
/**
* This class represents a control flow graph of a method.
*
* @version $Id: ControlFlowGraph.java,v 1.7 2004/12/15 08:28:55 conor Exp $
* @author <A HREF="http://www.inf.fu-berlin.de/~ehaase"/>Enver Haase</A>
*/
public class ControlFlowGraph{
/**
* Objects of this class represent a node in a ControlFlowGraph.
* These nodes are instructions, not basic blocks.
*/
private class InstructionContextImpl implements InstructionContext{
/**
* The TAG field is here for external temporary flagging, such
* as graph colouring.
*
* @see #getTag()
* @see #setTag(int)
*/
private int TAG;
/**
* The InstructionHandle this InstructionContext is wrapped around.
*/
private InstructionHandle instruction;
/**
* The 'incoming' execution Frames.
*/
private HashMap inFrames; // key: the last-executed JSR
/**
* The 'outgoing' execution Frames.
*/
private HashMap outFrames; // key: the last-executed JSR
/**
* The 'execution predecessors' - a list of type InstructionContext
* of those instances that have been execute()d before in that order.
*/
private ArrayList executionPredecessors = null; // Type: InstructionContext
/**
* Creates an InstructionHandleImpl object from an InstructionHandle.
* Creation of one per InstructionHandle suffices. Don't create more.
*/
public InstructionContextImpl(InstructionHandle inst){
if (inst == null) throw new AssertionViolatedException("Cannot instantiate InstructionContextImpl from NULL.");
instruction = inst;
inFrames = new java.util.HashMap();
outFrames = new java.util.HashMap();
}
/* Satisfies InstructionContext.getTag(). */
public int getTag(){
return TAG;
}
/* Satisfies InstructionContext.setTag(int). */
public void setTag(int tag){
TAG = tag;
}
/**
* Returns the exception handlers of this instruction.
*/
public ExceptionHandler[] getExceptionHandlers(){
return exceptionhandlers.getExceptionHandlers(getInstruction());
}
/**
* Returns a clone of the "outgoing" frame situation with respect to the given ExecutionChain.
*/
public Frame getOutFrame(ArrayList execChain){
executionPredecessors = execChain;
Frame org;
InstructionContext jsr = lastExecutionJSR();
org = (Frame) outFrames.get(jsr);
if (org == null){
throw new AssertionViolatedException("outFrame not set! This:\n"+this+"\nExecutionChain: "+getExecutionChain()+"\nOutFrames: '"+outFrames+"'.");
}
return org.getClone();
}
/**
* "Merges in" (vmspec2, page 146) the "incoming" frame situation;
* executes the instructions symbolically
* and therefore calculates the "outgoing" frame situation.
* Returns: True iff the "incoming" frame situation changed after
* merging with "inFrame".
* The execPreds ArrayList must contain the InstructionContext
* objects executed so far in the correct order. This is just
* one execution path [out of many]. This is needed to correctly
* "merge" in the special case of a RET's successor.
* <B>The InstConstraintVisitor and ExecutionVisitor instances
* must be set up correctly.</B>
* @return true - if and only if the "outgoing" frame situation
* changed from the one before execute()ing.
*/
public boolean execute(Frame inFrame, ArrayList execPreds, InstConstraintVisitor icv, ExecutionVisitor ev){
executionPredecessors = (ArrayList) execPreds.clone();
//sanity check
if ( (lastExecutionJSR() == null) && (subroutines.subroutineOf(getInstruction()) != subroutines.getTopLevel() ) ){
throw new AssertionViolatedException("Huh?! Am I '"+this+"' part of a subroutine or not?");
}
if ( (lastExecutionJSR() != null) && (subroutines.subroutineOf(getInstruction()) == subroutines.getTopLevel() ) ){
throw new AssertionViolatedException("Huh?! Am I '"+this+"' part of a subroutine or not?");
}
Frame inF = (Frame) inFrames.get(lastExecutionJSR());
if (inF == null){// no incoming frame was set, so set it.
inFrames.put(lastExecutionJSR(), inFrame);
inF = inFrame;
}
else{// if there was an "old" inFrame
if (inF.equals(inFrame)){ //shortcut: no need to merge equal frames.
return false;
}
if (! mergeInFrames(inFrame)){
return false;
}
}
// Now we're sure the inFrame has changed!
// new inFrame is already merged in, see above.
Frame workingFrame = inF.getClone();
try{
// This verifies the InstructionConstraint for the current
// instruction, but does not modify the workingFrame object.
//InstConstraintVisitor icv = InstConstraintVisitor.getInstance(VerifierFactory.getVerifier(method_gen.getClassName()));
icv.setFrame(workingFrame);
getInstruction().accept(icv);
}
catch(StructuralCodeConstraintException ce){
ce.extendMessage("","\nInstructionHandle: "+getInstruction()+"\n");
ce.extendMessage("","\nExecution Frame:\n"+workingFrame);
extendMessageWithFlow(ce);
throw ce;
}
// This executes the Instruction.
// Therefore the workingFrame object is modified.
//ExecutionVisitor ev = ExecutionVisitor.getInstance(VerifierFactory.getVerifier(method_gen.getClassName()));
ev.setFrame(workingFrame);
getInstruction().accept(ev);
//getInstruction().accept(ExecutionVisitor.withFrame(workingFrame));
outFrames.put(lastExecutionJSR(), workingFrame);
return true; // new inFrame was different from old inFrame so merging them
// yielded a different this.inFrame.
}
/**
* Returns a simple String representation of this InstructionContext.
*/
public String toString(){
//TODO: Put information in the brackets, e.g.
// Is this an ExceptionHandler? Is this a RET? Is this the start of
// a subroutine?
String ret = getInstruction().toString(false)+"\t[InstructionContext]";
return ret;
}
/**
* Does the actual merging (vmspec2, page 146).
* Returns true IFF this.inFrame was changed in course of merging with inFrame.
*/
private boolean mergeInFrames(Frame inFrame){
// TODO: Can be performance-improved.
Frame inF = (Frame) inFrames.get(lastExecutionJSR());
OperandStack oldstack = inF.getStack().getClone();
LocalVariables oldlocals = inF.getLocals().getClone();
try{
inF.getStack().merge(inFrame.getStack());
inF.getLocals().merge(inFrame.getLocals());
}
catch (StructuralCodeConstraintException sce){
extendMessageWithFlow(sce);
throw sce;
}
if ( oldstack.equals(inF.getStack()) &&
oldlocals.equals(inF.getLocals()) ){
return false;
}
else{
return true;
}
}
/**
* Returns the control flow execution chain. This is built
* while execute(Frame, ArrayList)-ing the code represented
* by the surrounding ControlFlowGraph.
*/
private String getExecutionChain(){
String s = this.toString();
for (int i=executionPredecessors.size()-1; i>=0; i--){
s = executionPredecessors.get(i)+"\n" + s;
}
return s;
}
/**
* Extends the StructuralCodeConstraintException ("e") object with an at-the-end-extended message.
* This extended message will then reflect the execution flow needed to get to the constraint
* violation that triggered the throwing of the "e" object.
*/
private void extendMessageWithFlow(StructuralCodeConstraintException e){
String s = "Execution flow:\n";
e.extendMessage("", s+getExecutionChain());
}
/*
* Fulfils the contract of InstructionContext.getInstruction().
*/
public InstructionHandle getInstruction(){
return instruction;
}
/**
* Returns the InstructionContextImpl with an JSR/JSR_W
* that was last in the ExecutionChain, without
* a corresponding RET, i.e.
* we were called by this one.
* Returns null if we were called from the top level.
*/
private InstructionContextImpl lastExecutionJSR(){
int size = executionPredecessors.size();
int retcount = 0;
for (int i=size-1; i>=0; i--){
InstructionContextImpl current = (InstructionContextImpl) (executionPredecessors.get(i));
Instruction currentlast = current.getInstruction().getInstruction();
if (currentlast instanceof RET) retcount++;
if (currentlast instanceof JsrInstruction){
retcount--;
if (retcount == -1) return current;
}
}
return null;
}
/* Satisfies InstructionContext.getSuccessors(). */
public InstructionContext[] getSuccessors(){
return contextsOf(_getSuccessors());
}
/**
* A utility method that calculates the successors of a given InstructionHandle
* That means, a RET does have successors as defined here.
* A JsrInstruction has its target as its successor
* (opposed to its physical successor) as defined here.
*/
// TODO: implement caching!
private InstructionHandle[] _getSuccessors(){
final InstructionHandle[] empty = new InstructionHandle[0];
final InstructionHandle[] single = new InstructionHandle[1];
final InstructionHandle[] pair = new InstructionHandle[2];
Instruction inst = getInstruction().getInstruction();
if (inst instanceof RET){
Subroutine s = subroutines.subroutineOf(getInstruction());
if (s==null){ //return empty; // RET in dead code. "empty" would be the correct answer, but we know something about the surrounding project...
throw new AssertionViolatedException("Asking for successors of a RET in dead code?!");
}
//TODO: remove. Only JustIce must not use it, but foreign users of the ControlFlowGraph
// will want it. Thanks Johannes Wust.
//throw new AssertionViolatedException("DID YOU REALLY WANT TO ASK FOR RET'S SUCCS?");
InstructionHandle[] jsrs = s.getEnteringJsrInstructions();
InstructionHandle[] ret = new InstructionHandle[jsrs.length];
for (int i=0; i<jsrs.length; i++){
ret[i] = jsrs[i].getNext();
}
return ret;
}
// Terminates method normally.
if (inst instanceof ReturnInstruction){
return empty;
}
// Terminates method abnormally, because JustIce mandates
// subroutines not to be protected by exception handlers.
if (inst instanceof ATHROW){
return empty;
}
// See method comment.
if (inst instanceof JsrInstruction){
single[0] = ((JsrInstruction) inst).getTarget();
return single;
}
if (inst instanceof GotoInstruction){
single[0] = ((GotoInstruction) inst).getTarget();
return single;
}
if (inst instanceof BranchInstruction){
if (inst instanceof Select){
// BCEL's getTargets() returns only the non-default targets,
// thanks to Eli Tilevich for reporting.
InstructionHandle[] matchTargets = ((Select) inst).getTargets();
InstructionHandle[] ret = new InstructionHandle[matchTargets.length+1];
ret[0] = ((Select) inst).getTarget();
System.arraycopy(matchTargets, 0, ret, 1, matchTargets.length);
return ret;
}
else{
pair[0] = getInstruction().getNext();
pair[1] = ((BranchInstruction) inst).getTarget();
return pair;
}
}
// default case: Fall through.
single[0] = getInstruction().getNext();
return single;
}
} // End Inner InstructionContextImpl Class.
/** The MethodGen object we're working on. */
private final MethodGen method_gen;
/** The Subroutines object for the method whose control flow is represented by this ControlFlowGraph. */
private final Subroutines subroutines;
/** The ExceptionHandlers object for the method whose control flow is represented by this ControlFlowGraph. */
private final ExceptionHandlers exceptionhandlers;
/** All InstructionContext instances of this ControlFlowGraph. */
private Hashtable instructionContexts = new Hashtable(); //keys: InstructionHandle, values: InstructionContextImpl
/**
* A Control Flow Graph.
*/
public ControlFlowGraph(MethodGen method_gen){
subroutines = new Subroutines(method_gen);
exceptionhandlers = new ExceptionHandlers(method_gen);
InstructionHandle[] instructionhandles = method_gen.getInstructionList().getInstructionHandles();
for (int i=0; i<instructionhandles.length; i++){
instructionContexts.put(instructionhandles[i], new InstructionContextImpl(instructionhandles[i]));
}
this.method_gen = method_gen;
}
/**
* Returns the InstructionContext of a given instruction.
*/
public InstructionContext contextOf(InstructionHandle inst){
InstructionContext ic = (InstructionContext) instructionContexts.get(inst);
if (ic == null){
throw new AssertionViolatedException("InstructionContext requested for an InstructionHandle that's not known!");
}
return ic;
}
/**
* Returns the InstructionContext[] of a given InstructionHandle[],
* in a naturally ordered manner.
*/
public InstructionContext[] contextsOf(InstructionHandle[] insts){
InstructionContext[] ret = new InstructionContext[insts.length];
for (int i=0; i<insts.length; i++){
ret[i] = contextOf(insts[i]);
}
return ret;
}
/**
* Returns an InstructionContext[] with all the InstructionContext instances
* for the method whose control flow is represented by this ControlFlowGraph
* <B>(NOT ORDERED!)</B>.
*/
public InstructionContext[] getInstructionContexts(){
InstructionContext[] ret = new InstructionContext[instructionContexts.values().size()];
return (InstructionContext[]) instructionContexts.values().toArray(ret);
}
/**
* Returns true, if and only if the said instruction is not reachable; that means,
* if it is not part of this ControlFlowGraph.
*/
public boolean isDead(InstructionHandle i){
return subroutines.subroutineOf(i) == null;
}
}