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