300 lines
12 KiB
Java
300 lines
12 KiB
Java
/***
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* ASM: a very small and fast Java bytecode manipulation framework
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* Copyright (c) 2000-2005 INRIA, France Telecom
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 3. Neither the name of the copyright holders nor the names of its
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* contributors may be used to endorse or promote products derived from
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* this software without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
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* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
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* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
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* THE POSSIBILITY OF SUCH DAMAGE.
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*/
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package org.objectweb.asm;
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/**
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* A label represents a position in the bytecode of a method. Labels are used
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* for jump, goto, and switch instructions, and for try catch blocks.
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*
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* @author Eric Bruneton
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*/
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public class Label {
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/**
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* The line number corresponding to this label, if known.
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*/
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int line;
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/**
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* Indicates if the position of this label is known.
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*/
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boolean resolved;
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/**
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* The position of this label in the code, if known.
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*/
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int position;
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/**
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* If the label position has been updated, after instruction resizing.
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*/
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boolean resized;
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/**
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* Number of forward references to this label, times two.
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*/
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private int referenceCount;
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/**
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* Informations about forward references. Each forward reference is
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* described by two consecutive integers in this array: the first one is the
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* position of the first byte of the bytecode instruction that contains the
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* forward reference, while the second is the position of the first byte of
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* the forward reference itself. In fact the sign of the first integer
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* indicates if this reference uses 2 or 4 bytes, and its absolute value
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* gives the position of the bytecode instruction.
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*/
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private int[] srcAndRefPositions;
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/*
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* Fields for the control flow graph analysis algorithm (used to compute the
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* maximum stack size). A control flow graph contains one node per "basic
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* block", and one edge per "jump" from one basic block to another. Each
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* node (i.e., each basic block) is represented by the Label object that
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* corresponds to the first instruction of this basic block. Each node also
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* stores the list of it successors in the graph, as a linked list of Edge
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* objects.
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*/
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/**
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* The stack size at the beginning of this basic block. This size is
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* initially unknown. It is computed by the control flow analysis algorithm
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* (see {@link MethodWriter#visitMaxs visitMaxs}).
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*/
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int beginStackSize;
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/**
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* The (relative) maximum stack size corresponding to this basic block. This
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* size is relative to the stack size at the beginning of the basic block,
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* i.e., the true maximum stack size is equal to {@link #beginStackSize
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* beginStackSize} + {@link #maxStackSize maxStackSize}.
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*/
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int maxStackSize;
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/**
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* The successors of this node in the control flow graph. These successors
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* are stored in a linked list of {@link Edge Edge} objects, linked to each
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* other by their {@link Edge#next} field.
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*/
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Edge successors;
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/**
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* The next basic block in the basic block stack. See
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* {@link MethodWriter#visitMaxs visitMaxs}.
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*/
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Label next;
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/**
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* <tt>true</tt> if this basic block has been pushed in the basic block
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* stack. See {@link MethodWriter#visitMaxs visitMaxs}.
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*/
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boolean pushed;
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// ------------------------------------------------------------------------
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// Constructor
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// ------------------------------------------------------------------------
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/**
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* Constructs a new label.
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*/
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public Label() {
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}
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// ------------------------------------------------------------------------
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// Methods to compute offsets and to manage forward references
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// ------------------------------------------------------------------------
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/**
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* Returns the offset corresponding to this label. This offset is computed
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* from the start of the method's bytecode. <i>This method is intended for
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* {@link Attribute} sub classes, and is normally not needed by class
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* generators or adapters.</i>
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*
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* @return the offset corresponding to this label.
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* @throws IllegalStateException if this label is not resolved yet.
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*/
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public int getOffset() {
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if (!resolved) {
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throw new IllegalStateException("Label offset position has not been resolved yet");
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}
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return position;
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}
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/**
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* Puts a reference to this label in the bytecode of a method. If the
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* position of the label is known, the offset is computed and written
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* directly. Otherwise, a null offset is written and a new forward reference
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* is declared for this label.
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*
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* @param owner the code writer that calls this method.
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* @param out the bytecode of the method.
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* @param source the position of first byte of the bytecode instruction that
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* contains this label.
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* @param wideOffset <tt>true</tt> if the reference must be stored in 4
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* bytes, or <tt>false</tt> if it must be stored with 2 bytes.
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* @throws IllegalArgumentException if this label has not been created by
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* the given code writer.
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*/
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void put(
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final MethodWriter owner,
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final ByteVector out,
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final int source,
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final boolean wideOffset)
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{
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if (resolved) {
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if (wideOffset) {
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out.putInt(position - source);
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} else {
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out.putShort(position - source);
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}
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} else {
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if (wideOffset) {
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addReference(-1 - source, out.length);
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out.putInt(-1);
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} else {
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addReference(source, out.length);
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out.putShort(-1);
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}
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}
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}
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/**
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* Adds a forward reference to this label. This method must be called only
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* for a true forward reference, i.e. only if this label is not resolved
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* yet. For backward references, the offset of the reference can be, and
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* must be, computed and stored directly.
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*
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* @param sourcePosition the position of the referencing instruction. This
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* position will be used to compute the offset of this forward
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* reference.
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* @param referencePosition the position where the offset for this forward
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* reference must be stored.
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*/
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private void addReference(
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final int sourcePosition,
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final int referencePosition)
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{
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if (srcAndRefPositions == null) {
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srcAndRefPositions = new int[6];
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}
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if (referenceCount >= srcAndRefPositions.length) {
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int[] a = new int[srcAndRefPositions.length + 6];
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System.arraycopy(srcAndRefPositions,
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0,
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a,
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0,
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srcAndRefPositions.length);
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srcAndRefPositions = a;
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}
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srcAndRefPositions[referenceCount++] = sourcePosition;
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srcAndRefPositions[referenceCount++] = referencePosition;
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}
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/**
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* Resolves all forward references to this label. This method must be called
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* when this label is added to the bytecode of the method, i.e. when its
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* position becomes known. This method fills in the blanks that where left
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* in the bytecode by each forward reference previously added to this label.
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*
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* @param owner the code writer that calls this method.
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* @param position the position of this label in the bytecode.
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* @param data the bytecode of the method.
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* @return <tt>true</tt> if a blank that was left for this label was to
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* small to store the offset. In such a case the corresponding jump
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* instruction is replaced with a pseudo instruction (using unused
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* opcodes) using an unsigned two bytes offset. These pseudo
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* instructions will need to be replaced with true instructions with
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* wider offsets (4 bytes instead of 2). This is done in
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* {@link MethodWriter#resizeInstructions}.
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* @throws IllegalArgumentException if this label has already been resolved,
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* or if it has not been created by the given code writer.
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*/
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boolean resolve(
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final MethodWriter owner,
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final int position,
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final byte[] data)
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{
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boolean needUpdate = false;
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this.resolved = true;
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this.position = position;
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int i = 0;
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while (i < referenceCount) {
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int source = srcAndRefPositions[i++];
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int reference = srcAndRefPositions[i++];
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int offset;
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if (source >= 0) {
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offset = position - source;
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if (offset < Short.MIN_VALUE || offset > Short.MAX_VALUE) {
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/*
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* changes the opcode of the jump instruction, in order to
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* be able to find it later (see resizeInstructions in
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* MethodWriter). These temporary opcodes are similar to
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* jump instruction opcodes, except that the 2 bytes offset
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* is unsigned (and can therefore represent values from 0 to
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* 65535, which is sufficient since the size of a method is
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* limited to 65535 bytes).
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*/
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int opcode = data[reference - 1] & 0xFF;
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if (opcode <= Opcodes.JSR) {
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// changes IFEQ ... JSR to opcodes 202 to 217
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data[reference - 1] = (byte) (opcode + 49);
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} else {
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// changes IFNULL and IFNONNULL to opcodes 218 and 219
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data[reference - 1] = (byte) (opcode + 20);
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}
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needUpdate = true;
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}
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data[reference++] = (byte) (offset >>> 8);
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data[reference] = (byte) offset;
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} else {
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offset = position + source + 1;
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data[reference++] = (byte) (offset >>> 24);
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data[reference++] = (byte) (offset >>> 16);
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data[reference++] = (byte) (offset >>> 8);
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data[reference] = (byte) offset;
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}
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}
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return needUpdate;
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}
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// ------------------------------------------------------------------------
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// Overriden Object methods
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// ------------------------------------------------------------------------
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/**
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* Returns a string representation of this label.
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*
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* @return a string representation of this label.
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*/
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public String toString() {
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return "L" + System.identityHashCode(this);
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}
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}
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