/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You 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 org.apache.bcel.generic.ObjectType;
import org.apache.bcel.generic.ReferenceType;
import org.apache.bcel.generic.Type;
import org.apache.bcel.verifier.exc.AssertionViolatedException;
import org.apache.bcel.verifier.exc.StructuralCodeConstraintException;
/**
* This class implements a stack used for symbolic JVM stack simulation.
* [It's used an an operand stack substitute.]
* Elements of this stack are org.apache.bcel.generic.Type objects.
*
* @version $Id: OperandStack.java 1598766 2014-05-30 22:51:27Z sebb $
* @author Enver Haase
*/
public class OperandStack{
/** We hold the stack information here. */
private ArrayList<Type> stack = new ArrayList<Type>();
/** The maximum number of stack slots this OperandStack instance may hold. */
private int maxStack;
/**
* Creates an empty stack with a maximum of maxStack slots.
*/
public OperandStack(int maxStack){
this.maxStack = maxStack;
}
/**
* Creates an otherwise empty stack with a maximum of maxStack slots and
* the ObjectType 'obj' at the top.
*/
public OperandStack(int maxStack, ObjectType obj){
this.maxStack = maxStack;
this.push(obj);
}
/**
* Returns a deep copy of this object; that means, the clone operates
* on a new stack. However, the Type objects on the stack are
* shared.
*/
@Override
protected Object clone(){
OperandStack newstack = new OperandStack(this.maxStack);
newstack.stack = (ArrayList<Type>) this.stack.clone();
return newstack;
}
/**
* Clears the stack.
*/
public void clear(){
stack = new ArrayList<Type>();
}
/** @return a hash code value for the object.
*/
@Override
public int hashCode() { return stack.hashCode(); }
/**
* Returns true if and only if this OperandStack
* equals another, meaning equal lengths and equal
* objects on the stacks.
*/
@Override
public boolean equals(Object o){
if (!(o instanceof OperandStack)) {
return false;
}
OperandStack s = (OperandStack) o;
return this.stack.equals(s.stack);
}
/**
* Returns a (typed!) clone of this.
*
* @see #clone()
*/
public OperandStack getClone(){
return (OperandStack) this.clone();
}
/**
* Returns true IFF this OperandStack is empty.
*/
public boolean isEmpty(){
return stack.isEmpty();
}
/**
* Returns the number of stack slots this stack can hold.
*/
public int maxStack(){
return this.maxStack;
}
/**
* Returns the element on top of the stack. The element is not popped off the stack!
*/
public Type peek(){
return peek(0);
}
/**
* Returns the element that's i elements below the top element; that means,
* iff i==0 the top element is returned. The element is not popped off the stack!
*/
public Type peek(int i){
return stack.get(size()-i-1);
}
/**
* Returns the element on top of the stack. The element is popped off the stack.
*/
public Type pop(){
Type e = stack.remove(size()-1);
return e;
}
/**
* Pops i elements off the stack. ALWAYS RETURNS "null"!!!
*/
public Type pop(int i){
for (int j=0; j<i; j++){
pop();
}
return null;
}
/**
* Pushes a Type object onto the stack.
*/
public void push(Type type){
if (type == null) {
throw new AssertionViolatedException("Cannot push NULL onto OperandStack.");
}
if (type == Type.BOOLEAN || type == Type.CHAR || type == Type.BYTE || type == Type.SHORT){
throw new AssertionViolatedException("The OperandStack does not know about '"+type+"'; use Type.INT instead.");
}
if (slotsUsed() >= maxStack){
throw new AssertionViolatedException("OperandStack too small, should have thrown proper Exception elsewhere. Stack: "+this);
}
stack.add(type);
}
/**
* Returns the size of this OperandStack; that means, how many Type objects there are.
*/
public int size(){
return stack.size();
}
/**
* Returns the number of stack slots used.
* @see #maxStack()
*/
public int slotsUsed(){
/* XXX change this to a better implementation using a variable
that keeps track of the actual slotsUsed()-value monitoring
all push()es and pop()s.
*/
int slots = 0;
for (int i=0; i<stack.size(); i++){
slots += peek(i).getSize();
}
return slots;
}
/**
* Returns a String representation of this OperandStack instance.
*/
@Override
public String toString(){
StringBuilder sb = new StringBuilder();
sb.append("Slots used: ");
sb.append(slotsUsed());
sb.append(" MaxStack: ");
sb.append(maxStack);
sb.append(".\n");
for (int i=0; i<size(); i++){
sb.append(peek(i));
sb.append(" (Size: ");
sb.append(String.valueOf(peek(i).getSize()));
sb.append(")\n");
}
return sb.toString();
}
/**
* Merges another stack state into this instance's stack state.
* See the Java Virtual Machine Specification, Second Edition, page 146: 4.9.2
* for details.
*/
public void merge(OperandStack s){
try {
if ( (slotsUsed() != s.slotsUsed()) || (size() != s.size()) ) {
throw new StructuralCodeConstraintException("Cannot merge stacks of different size:\nOperandStack A:\n"+this+"\nOperandStack B:\n"+s);
}
for (int i=0; i<size(); i++){
// If the object _was_ initialized and we're supposed to merge
// in some uninitialized object, we reject the code (see vmspec2, 4.9.4, last paragraph).
if ( (! (stack.get(i) instanceof UninitializedObjectType)) && (s.stack.get(i) instanceof UninitializedObjectType) ){
throw new StructuralCodeConstraintException("Backwards branch with an uninitialized object on the stack detected.");
}
// Even harder, we're not initialized but are supposed to broaden
// the known object type
if ( (!(stack.get(i).equals(s.stack.get(i)))) && (stack.get(i) instanceof UninitializedObjectType) && (!(s.stack.get(i) instanceof UninitializedObjectType))){
throw new StructuralCodeConstraintException("Backwards branch with an uninitialized object on the stack detected.");
}
// on the other hand...
if (stack.get(i) instanceof UninitializedObjectType){ //if we have an uninitialized object here
if (! (s.stack.get(i) instanceof UninitializedObjectType)){ //that has been initialized by now
stack.set(i, ((UninitializedObjectType) (stack.get(i))).getInitialized() ); //note that.
}
}
if (! stack.get(i).equals(s.stack.get(i))){
if ( (stack.get(i) instanceof ReferenceType) &&
(s.stack.get(i) instanceof ReferenceType) ){
stack.set(i, ((ReferenceType) stack.get(i)).getFirstCommonSuperclass((ReferenceType) (s.stack.get(i))));
}
else{
throw new StructuralCodeConstraintException("Cannot merge stacks of different types:\nStack A:\n"+this+"\nStack B:\n"+s);
}
}
}
} catch (ClassNotFoundException e) {
// FIXME: maybe not the best way to handle this
throw new AssertionViolatedException("Missing class: " + e, e);
}
}
/**
* Replaces all occurences of u in this OperandStack instance
* with an "initialized" ObjectType.
*/
public void initializeObject(UninitializedObjectType u){
for (int i=0; i<stack.size(); i++){
if (stack.get(i) == u){
stack.set(i, u.getInitialized());
}
}
}
}