src/main/java/org/apache/bcel/verifier/structurals/OperandStack.java - commons-bcel - Git at Google

 /*
  * 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 as an operand stack substitute.]
  * Elements of this stack are {@link Type} objects.
  */
 public class OperandStack implements Cloneable {

     /** We hold the stack information here. */
     private ArrayList<Type> stack = new ArrayList<>();

     /** The maximum number of stack slots this OperandStack instance may hold. */
     private final int maxStack;

     /**
      * Creates an empty stack with a maximum of maxStack slots.
      */
     public OperandStack(final 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(final int maxStack, final ObjectType obj) {
         this.maxStack = maxStack;
         this.push(obj);
     }

     /**
      * Clears the stack.
      */
     public void clear() {
         stack = new ArrayList<>();
     }

     /**
      * 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
     public Object clone() {
         final OperandStack newstack = new OperandStack(this.maxStack);
         @SuppressWarnings("unchecked") // OK because this.stack is the same type
         final ArrayList<Type> clone = (ArrayList<Type>) this.stack.clone();
         newstack.stack = clone;
         return newstack;
     }

     /**
      * Returns true if and only if this OperandStack equals another, meaning equal lengths and equal objects on the stacks.
      */
     @Override
     public boolean equals(final Object o) {
         if (!(o instanceof OperandStack)) {
             return false;
         }
         final 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();
     }

     /**
      * @return a hash code value for the object.
      */
     @Override
     public int hashCode() {
         return stack.hashCode();
     }

     /**
      * Replaces all occurrences of u in this OperandStack instance with an "initialized" ObjectType.
      */
     public void initializeObject(final UninitializedObjectType u) {
         for (int i = 0; i < stack.size(); i++) {
             if (stack.get(i) == u) {
                 stack.set(i, u.getInitialized());
             }
         }
     }

     /**
      * 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;
     }

     /**
      * 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(final 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 && !(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)) {
                         throw new StructuralCodeConstraintException("Cannot merge stacks of different types:\nStack A:\n" + this + "\nStack B:\n" + s);
                     }
                     stack.set(i, ((ReferenceType) stack.get(i)).getFirstCommonSuperclass((ReferenceType) s.stack.get(i)));
                 }
             }
         } catch (final ClassNotFoundException e) {
             // FIXME: maybe not the best way to handle this
             throw new AssertionViolatedException("Missing class: " + e, e);
         }
     }

     /**
      * 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(final 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() {
         return stack.remove(size() - 1);
     }

     /**
      * Pops i elements off the stack. Always returns null.
      *
      * @return Always returns null.
      */
     public Type pop(final int count) {
         for (int j = 0; j < count; j++) {
             pop();
         }
         return null;
     }

     /**
      * Pushes a Type object onto the stack.
      */
     public void push(final 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() {
         final 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();
     }

 }
	/*
	* 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 as an operand stack substitute.]
	* Elements of this stack are {@link Type} objects.
	*/
	public class OperandStack implements Cloneable {

	/** We hold the stack information here. */
	private ArrayList<Type> stack = new ArrayList<>();

	/** The maximum number of stack slots this OperandStack instance may hold. */
	private final int maxStack;

	/**
	* Creates an empty stack with a maximum of maxStack slots.
	*/
	public OperandStack(final 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(final int maxStack, final ObjectType obj) {
	this.maxStack = maxStack;
	this.push(obj);
	}

	/**
	* Clears the stack.
	*/
	public void clear() {
	stack = new ArrayList<>();
	}

	/**
	* 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
	public Object clone() {
	final OperandStack newstack = new OperandStack(this.maxStack);
	@SuppressWarnings("unchecked") // OK because this.stack is the same type
	final ArrayList<Type> clone = (ArrayList<Type>) this.stack.clone();
	newstack.stack = clone;
	return newstack;
	}

	/**
	* Returns true if and only if this OperandStack equals another, meaning equal lengths and equal objects on the stacks.
	*/
	@Override
	public boolean equals(final Object o) {
	if (!(o instanceof OperandStack)) {
	return false;
	}
	final 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();
	}

	/**
	* @return a hash code value for the object.
	*/
	@Override
	public int hashCode() {
	return stack.hashCode();
	}

	/**
	* Replaces all occurrences of u in this OperandStack instance with an "initialized" ObjectType.
	*/
	public void initializeObject(final UninitializedObjectType u) {
	for (int i = 0; i < stack.size(); i++) {
	if (stack.get(i) == u) {
	stack.set(i, u.getInitialized());
	}
	}
	}

	/**
	* 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;
	}

	/**
	* 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(final 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 && !(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)) {
	throw new StructuralCodeConstraintException("Cannot merge stacks of different types:\nStack A:\n" + this + "\nStack B:\n" + s);
	}
	stack.set(i, ((ReferenceType) stack.get(i)).getFirstCommonSuperclass((ReferenceType) s.stack.get(i)));
	}
	}
	} catch (final ClassNotFoundException e) {
	// FIXME: maybe not the best way to handle this
	throw new AssertionViolatedException("Missing class: " + e, e);
	}
	}

	/**
	* 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(final 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() {
	return stack.remove(size() - 1);
	}

	/**
	* Pops i elements off the stack. Always returns null.
	*
	* @return Always returns null.
	*/
	public Type pop(final int count) {
	for (int j = 0; j < count; j++) {
	pop();
	}
	return null;
	}

	/**
	* Pushes a Type object onto the stack.
	*/
	public void push(final 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() {
	final 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();
	}

	}