    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..
    027 * Branch instructions may have a variable length, namely GOTO, JSR,
    028 * LOOKUPSWITCH and TABLESWITCH.
    029 *
    030 * @see InstructionList
    031 */
    032public abstract class BranchInstruction extends Instruction implements InstructionTargeter {
    033
    034    /**
    035     * @deprecated (since 6.0) will be made private; do not access directly, use getter/setter
    036     */
    037    @Deprecated
    038    protected int index; // Branch target relative to this instruction
    039
    040    /**
    041     * @deprecated (since 6.0) will be made private; do not access directly, use getter/setter
    042     */
    043    @Deprecated
    044    protected InstructionHandle target; // Target object in instruction list
    045
    046    /**
    047     * @deprecated (since 6.0) will be made private; do not access directly, use getter/setter
    048     */
    049    @Deprecated
    050    protected int position; // Byte code offset
    051
    052
    053    /**
    054     * Empty constructor needed for Instruction.readInstruction.
    055     * Not to be used otherwise.
    056     */
    057    BranchInstruction() {
    058    }
    059
    060
    061    /** Common super constructor
    062     * @param opcode Instruction opcode
    063     * @param target instruction to branch to
    064     */
    065    protected BranchInstruction(final short opcode, final InstructionHandle target) {
    066        super(opcode, (short) 3);
    067        setTarget(target);
    068    }
    069
    070
    071    /**
    072     * Dump instruction as byte code to stream out.
    073     * @param out Output stream
    074     */
    075    @Override
    076    public void dump( final DataOutputStream out ) throws IOException {
    077        out.writeByte(super.getOpcode());
    078        index = getTargetOffset();
    079        if (!isValidShort(index)) {
    080            throw new ClassGenException("Branch target offset too large for short: " + index);
    081        }
    082        out.writeShort(index); // May be negative, i.e., point backwards
    083    }
    084
    085
    086    /**
    087     * @param _target branch target
    088     * @return the offset to  `target' relative to this instruction
    089     */
    090    protected int getTargetOffset( final InstructionHandle _target ) {
    091        if (_target == null) {
    092            throw new ClassGenException("Target of " + super.toString(true)
    093                    + " is invalid null handle");
    094        }
    095        final int t = _target.getPosition();
    096        if (t < 0) {
    097            throw new ClassGenException("Invalid branch target position offset for "
    098                    + super.toString(true) + ":" + t + ":" + _target);
    099        }
    100        return t - position;
    101    }
    102
    103
    104    /**
    105     * @return the offset to this instruction's target
    106     */
    107    protected int getTargetOffset() {
    108        return getTargetOffset(target);
    109    }
    110
    111
    112    /**
    113     * Called by InstructionList.setPositions when setting the position for every
    114     * instruction. In the presence of variable length instructions `setPositions'
    115     * performs multiple passes over the instruction list to calculate the
    116     * correct (byte) positions and offsets by calling this function.
    117     *
    118     * @param offset additional offset caused by preceding (variable length) instructions
    119     * @param max_offset the maximum offset that may be caused by these instructions
    120     * @return additional offset caused by possible change of this instruction's length
    121     */
    122    protected int updatePosition( final int offset, final int max_offset ) {
    123        position += offset;
    124        return 0;
    125    }
    126
    127
    128    /**
    129     * Long output format:
    130     *
    131     * &lt;position in byte code&gt;
    132     * &lt;name of opcode&gt; "["&lt;opcode number&gt;"]"
    133     * "("&lt;length of instruction&gt;")"
    134     * "&lt;"&lt;target instruction&gt;"&gt;" "@"&lt;branch target offset&gt;
    135     *
    136     * @param verbose long/short format switch
    137     * @return mnemonic for instruction
    138     */
    139    @Override
    140    public String toString( final boolean verbose ) {
    141        final String s = super.toString(verbose);
    142        String t = "null";
    143        if (verbose) {
    144            if (target != null) {
    145                if (target.getInstruction() == this) {
    146                    t = "<points to itself>";
    147                } else if (target.getInstruction() == null) {
    148                    t = "<null instruction!!!?>";
    149                } else {
    150                    // I'm more interested in the address of the target then
    151                    // the instruction located there.
    152                    //t = target.getInstruction().toString(false); // Avoid circles
    153                    t = "" + target.getPosition();
    154                }
    155            }
    156        } else {
    157            if (target != null) {
    158                index = target.getPosition();
    159                // index = getTargetOffset();  crashes if positions haven't been set
    160                // t = "" + (index + position);
    161                t = "" + index;
    162            }
    163        }
    164        return s + " -> " + t;
    165    }
    166
    167
    168    /**
    169     * Read needed data (e.g. index) from file. Conversion to a InstructionHandle
    170     * is done in InstructionList(byte[]).
    171     *
    172     * @param bytes input stream
    173     * @param wide wide prefix?
    174     * @see InstructionList
    175     */
    176    @Override
    177    protected void initFromFile( final ByteSequence bytes, final boolean wide ) throws IOException {
    178        super.setLength(3);
    179        index = bytes.readShort();
    180    }
    181
    182
    183    /**
    184     * @return target offset in byte code
    185     */
    186    public final int getIndex() {
    187        return index;
    188    }
    189
    190
    191    /**
    192     * @return target of branch instruction
    193     */
    194    public InstructionHandle getTarget() {
    195        return target;
    196    }
    197
    198
    199    /**
    200     * Set branch target
    201     * @param target branch target
    202     */
    203    public void setTarget( final InstructionHandle target ) {
    204        notifyTarget(this.target, target, this);
    205        this.target = target;
    206    }
    207
    208
    209    /**
    210     * Used by BranchInstruction, LocalVariableGen, CodeExceptionGen, LineNumberGen
    211     */
    212    static void notifyTarget( final InstructionHandle old_ih, final InstructionHandle new_ih,
    213            final InstructionTargeter t ) {
    214        if (old_ih != null) {
    215            old_ih.removeTargeter(t);
    216        }
    217        if (new_ih != null) {
    218            new_ih.addTargeter(t);
    219        }
    220    }
    221
    222
    223    /**
    224     * @param old_ih old target
    225     * @param new_ih new target
    226     */
    227    @Override
    228    public void updateTarget( final InstructionHandle old_ih, final InstructionHandle new_ih ) {
    229        if (target == old_ih) {
    230            setTarget(new_ih);
    231        } else {
    232            throw new ClassGenException("Not targeting " + old_ih + ", but " + target);
    233        }
    234    }
    235
    236
    237    /**
    238     * @return true, if ih is target of this instruction
    239     */
    240    @Override
    241    public boolean containsTarget( final InstructionHandle ih ) {
    242        return target == ih;
    243    }
    244
    245
    246    /**
    247     * Inform target that it's not targeted anymore.
    248     */
    249    @Override
    250    void dispose() {
    251        setTarget(null);
    252        index = -1;
    253        position = -1;
    254    }
    255
    256
    257    /**
    258     * @return the position
    259     * @since 6.0
    260     */
    261    protected int getPosition() {
    262        return position;
    263    }
    264
    265
    266    /**
    267     * @param position the position to set
    268     * @since 6.0
    269     */
    270    protected void setPosition(final int position) {
    271        this.position = position;
    272    }
    273
    274
    275    /**
    276     * @param index the index to set
    277     * @since 6.0
    278     */
    279    protected void setIndex(final int index) {
    280        this.index = index;
    281    }
    282
    283}