BranchInstruction.java
/*
* 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.generic;
import java.io.DataOutputStream;
import java.io.IOException;
import org.apache.bcel.util.ByteSequence;
/**
* Abstract super class for branching instructions like GOTO, IFEQ, etc.. Branch instructions may have a variable
* length, namely GOTO, JSR, LOOKUPSWITCH and TABLESWITCH.
*
* @see InstructionList
*/
public abstract class BranchInstruction extends Instruction implements InstructionTargeter {
/**
* Used by BranchInstruction, LocalVariableGen, CodeExceptionGen, LineNumberGen
*/
static void notifyTarget(final InstructionHandle oldIh, final InstructionHandle newIh, final InstructionTargeter t) {
if (oldIh != null) {
oldIh.removeTargeter(t);
}
if (newIh != null) {
newIh.addTargeter(t);
}
}
/**
* @deprecated (since 6.0) will be made private; do not access directly, use getter/setter
*/
@Deprecated
protected int index; // Branch target relative to this instruction
/**
* @deprecated (since 6.0) will be made private; do not access directly, use getter/setter
*/
@Deprecated
protected InstructionHandle target; // Target object in instruction list
/**
* @deprecated (since 6.0) will be made private; do not access directly, use getter/setter
*/
@Deprecated
protected int position; // Byte code offset
/**
* Empty constructor needed for Instruction.readInstruction. Not to be used otherwise.
*/
BranchInstruction() {
}
/**
* Common super constructor
*
* @param opcode Instruction opcode
* @param target instruction to branch to
*/
protected BranchInstruction(final short opcode, final InstructionHandle target) {
super(opcode, (short) 3);
setTarget(target);
}
/**
* @return true, if ih is target of this instruction
*/
@Override
public boolean containsTarget(final InstructionHandle ih) {
return target == ih;
}
/**
* Inform target that it's not targeted anymore.
*/
@Override
void dispose() {
setTarget(null);
index = -1;
position = -1;
}
/**
* Dump instruction as byte code to stream out.
*
* @param out Output stream
*/
@Override
public void dump(final DataOutputStream out) throws IOException {
out.writeByte(super.getOpcode());
index = getTargetOffset();
if (!isValidShort(index)) {
throw new ClassGenException("Branch target offset too large for short: " + index);
}
out.writeShort(index); // May be negative, i.e., point backwards
}
/**
* @return target offset in byte code
*/
public final int getIndex() {
return index;
}
/**
* @return the position
* @since 6.0
*/
protected int getPosition() {
return position;
}
/**
* @return target of branch instruction
*/
public InstructionHandle getTarget() {
return target;
}
/**
* @return the offset to this instruction's target
*/
protected int getTargetOffset() {
return getTargetOffset(target);
}
/**
* @param target branch target
* @return the offset to 'target' relative to this instruction
*/
protected int getTargetOffset(final InstructionHandle target) {
if (target == null) {
throw new ClassGenException("Target of " + super.toString(true) + " is invalid null handle");
}
final int t = target.getPosition();
if (t < 0) {
throw new ClassGenException("Invalid branch target position offset for " + super.toString(true) + ":" + t + ":" + target);
}
return t - position;
}
/**
* Read needed data (e.g. index) from file. Conversion to a InstructionHandle is done in InstructionList(byte[]).
*
* @param bytes input stream
* @param wide wide prefix?
* @see InstructionList
*/
@Override
protected void initFromFile(final ByteSequence bytes, final boolean wide) throws IOException {
super.setLength(3);
index = bytes.readShort();
}
/**
* @param index the index to set
* @since 6.0
*/
protected void setIndex(final int index) {
this.index = index;
}
/**
* @param position the position to set
* @since 6.0
*/
protected void setPosition(final int position) {
this.position = position;
}
/**
* Sets branch target
*
* @param target branch target
*/
public void setTarget(final InstructionHandle target) {
notifyTarget(this.target, target, this);
this.target = target;
}
/**
* Long output format:
*
* <position in byte code> <name of opcode> "["<opcode number>"]" "("<length of instruction>")"
* "<"<target instruction>">" "@"<branch target offset>
*
* @param verbose long/short format switch
* @return mnemonic for instruction
*/
@Override
public String toString(final boolean verbose) {
final String s = super.toString(verbose);
String t = "null";
if (target != null) {
if (verbose) {
if (target.getInstruction() == this) {
t = "<points to itself>";
} else if (target.getInstruction() == null) {
t = "<null instruction!!!?>";
} else {
// I'm more interested in the address of the target then
// the instruction located there.
// t = target.getInstruction().toString(false); // Avoid circles
t = "" + target.getPosition();
}
} else {
index = target.getPosition();
// index = getTargetOffset(); crashes if positions haven't been set
// t = "" + (index + position);
t = "" + index;
}
}
return s + " -> " + t;
}
/**
* Called by InstructionList.setPositions when setting the position for every instruction. In the presence of variable
* length instructions 'setPositions' performs multiple passes over the instruction list to calculate the correct (byte)
* positions and offsets by calling this function.
*
* @param offset additional offset caused by preceding (variable length) instructions
* @param maxOffset the maximum offset that may be caused by these instructions
* @return additional offset caused by possible change of this instruction's length
*/
protected int updatePosition(final int offset, final int maxOffset) {
position += offset;
return 0;
}
/**
* @param oldIh old target
* @param newIh new target
*/
@Override
public void updateTarget(final InstructionHandle oldIh, final InstructionHandle newIh) {
if (target != oldIh) {
throw new ClassGenException("Not targeting " + oldIh + ", but " + target);
}
setTarget(newIh);
}
}