    001/*
    002 * Licensed to the Apache Software Foundation (ASF) under one or more
    003 * contributor license agreements.  See the NOTICE file distributed with
    004 * this work for additional information regarding copyright ownership.
    005 * The ASF licenses this file to You under the Apache License, Version 2.0
    006 * (the "License"); you may not use this file except in compliance with
    007 * the License.  You may obtain a copy of the License at
    008 *
    009 *      http://www.apache.org/licenses/LICENSE-2.0
    010 *
    011 *  Unless required by applicable law or agreed to in writing, software
    012 *  distributed under the License is distributed on an "AS IS" BASIS,
    013 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    014 *  See the License for the specific language governing permissions and
    015 *  limitations under the License.
    016 *
    017 */
    018package org.apache.bcel.generic;
    019
    020import java.io.DataOutputStream;
    021import java.io.IOException;
    022
    023import org.apache.bcel.util.ByteSequence;
    024
    025/**
    026 * Abstract super class for branching instructions like GOTO, IFEQ, etc.. Branch instructions may have a variable
    027 * length, namely GOTO, JSR, LOOKUPSWITCH and TABLESWITCH.
    028 *
    029 * @see InstructionList
    030 */
    031public abstract class BranchInstruction extends Instruction implements InstructionTargeter {
    032
    033    /**
    034     * Used by BranchInstruction, LocalVariableGen, CodeExceptionGen, LineNumberGen
    035     */
    036    static void notifyTarget(final InstructionHandle old_ih, final InstructionHandle new_ih, final InstructionTargeter t) {
    037        if (old_ih != null) {
    038            old_ih.removeTargeter(t);
    039        }
    040        if (new_ih != null) {
    041            new_ih.addTargeter(t);
    042        }
    043    }
    044
    045    /**
    046     * @deprecated (since 6.0) will be made private; do not access directly, use getter/setter
    047     */
    048    @Deprecated
    049    protected int index; // Branch target relative to this instruction
    050
    051    /**
    052     * @deprecated (since 6.0) will be made private; do not access directly, use getter/setter
    053     */
    054    @Deprecated
    055    protected InstructionHandle target; // Target object in instruction list
    056
    057    /**
    058     * @deprecated (since 6.0) will be made private; do not access directly, use getter/setter
    059     */
    060    @Deprecated
    061    protected int position; // Byte code offset
    062
    063    /**
    064     * Empty constructor needed for Instruction.readInstruction. Not to be used otherwise.
    065     */
    066    BranchInstruction() {
    067    }
    068
    069    /**
    070     * Common super constructor
    071     *
    072     * @param opcode Instruction opcode
    073     * @param target instruction to branch to
    074     */
    075    protected BranchInstruction(final short opcode, final InstructionHandle target) {
    076        super(opcode, (short) 3);
    077        setTarget(target);
    078    }
    079
    080    /**
    081     * @return true, if ih is target of this instruction
    082     */
    083    @Override
    084    public boolean containsTarget(final InstructionHandle ih) {
    085        return target == ih;
    086    }
    087
    088    /**
    089     * Inform target that it's not targeted anymore.
    090     */
    091    @Override
    092    void dispose() {
    093        setTarget(null);
    094        index = -1;
    095        position = -1;
    096    }
    097
    098    /**
    099     * Dump instruction as byte code to stream out.
    100     *
    101     * @param out Output stream
    102     */
    103    @Override
    104    public void dump(final DataOutputStream out) throws IOException {
    105        out.writeByte(super.getOpcode());
    106        index = getTargetOffset();
    107        if (!isValidShort(index)) {
    108            throw new ClassGenException("Branch target offset too large for short: " + index);
    109        }
    110        out.writeShort(index); // May be negative, i.e., point backwards
    111    }
    112
    113    /**
    114     * @return target offset in byte code
    115     */
    116    public final int getIndex() {
    117        return index;
    118    }
    119
    120    /**
    121     * @return the position
    122     * @since 6.0
    123     */
    124    protected int getPosition() {
    125        return position;
    126    }
    127
    128    /**
    129     * @return target of branch instruction
    130     */
    131    public InstructionHandle getTarget() {
    132        return target;
    133    }
    134
    135    /**
    136     * @return the offset to this instruction's target
    137     */
    138    protected int getTargetOffset() {
    139        return getTargetOffset(target);
    140    }
    141
    142    /**
    143     * @param target branch target
    144     * @return the offset to `target' relative to this instruction
    145     */
    146    protected int getTargetOffset(final InstructionHandle target) {
    147        if (target == null) {
    148            throw new ClassGenException("Target of " + super.toString(true) + " is invalid null handle");
    149        }
    150        final int t = target.getPosition();
    151        if (t < 0) {
    152            throw new ClassGenException("Invalid branch target position offset for " + super.toString(true) + ":" + t + ":" + target);
    153        }
    154        return t - position;
    155    }
    156
    157    /**
    158     * Read needed data (e.g. index) from file. Conversion to a InstructionHandle is done in InstructionList(byte[]).
    159     *
    160     * @param bytes input stream
    161     * @param wide wide prefix?
    162     * @see InstructionList
    163     */
    164    @Override
    165    protected void initFromFile(final ByteSequence bytes, final boolean wide) throws IOException {
    166        super.setLength(3);
    167        index = bytes.readShort();
    168    }
    169
    170    /**
    171     * @param index the index to set
    172     * @since 6.0
    173     */
    174    protected void setIndex(final int index) {
    175        this.index = index;
    176    }
    177
    178    /**
    179     * @param position the position to set
    180     * @since 6.0
    181     */
    182    protected void setPosition(final int position) {
    183        this.position = position;
    184    }
    185
    186    /**
    187     * Set branch target
    188     *
    189     * @param target branch target
    190     */
    191    public void setTarget(final InstructionHandle target) {
    192        notifyTarget(this.target, target, this);
    193        this.target = target;
    194    }
    195
    196    /**
    197     * Long output format:
    198     *
    199     * &lt;position in byte code&gt; &lt;name of opcode&gt; "["&lt;opcode number&gt;"]" "("&lt;length of instruction&gt;")"
    200     * "&lt;"&lt;target instruction&gt;"&gt;" "@"&lt;branch target offset&gt;
    201     *
    202     * @param verbose long/short format switch
    203     * @return mnemonic for instruction
    204     */
    205    @Override
    206    public String toString(final boolean verbose) {
    207        final String s = super.toString(verbose);
    208        String t = "null";
    209        if (target != null) {
    210            if (verbose) {
    211                if (target.getInstruction() == this) {
    212                    t = "<points to itself>";
    213                } else if (target.getInstruction() == null) {
    214                    t = "<null instruction!!!?>";
    215                } else {
    216                    // I'm more interested in the address of the target then
    217                    // the instruction located there.
    218                    // t = target.getInstruction().toString(false); // Avoid circles
    219                    t = "" + target.getPosition();
    220                }
    221            } else {
    222                index = target.getPosition();
    223                // index = getTargetOffset(); crashes if positions haven't been set
    224                // t = "" + (index + position);
    225                t = "" + index;
    226            }
    227        }
    228        return s + " -> " + t;
    229    }
    230
    231    /**
    232     * Called by InstructionList.setPositions when setting the position for every instruction. In the presence of variable
    233     * length instructions `setPositions' performs multiple passes over the instruction list to calculate the correct (byte)
    234     * positions and offsets by calling this function.
    235     *
    236     * @param offset additional offset caused by preceding (variable length) instructions
    237     * @param max_offset the maximum offset that may be caused by these instructions
    238     * @return additional offset caused by possible change of this instruction's length
    239     */
    240    protected int updatePosition(final int offset, final int max_offset) {
    241        position += offset;
    242        return 0;
    243    }
    244
    245    /**
    246     * @param old_ih old target
    247     * @param new_ih new target
    248     */
    249    @Override
    250    public void updateTarget(final InstructionHandle old_ih, final InstructionHandle new_ih) {
    251        if (target != old_ih) {
    252            throw new ClassGenException("Not targeting " + old_ih + ", but " + target);
    253        }
    254        setTarget(new_ih);
    255    }
    256
    257}