/***
* ASM: a very small and fast Java bytecode manipulation framework
* Copyright (C) 2000 INRIA, France Telecom
* Copyright (C) 2002 France Telecom
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*
* Contact: Eric.Bruneton@rd.francetelecom.com
*
* Author: Eric Bruneton
*/
package org.gjt.sp.jedit.bsh.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.
*/
public class Label {
/**
* The code writer to which this label belongs, or <tt>null</tt> if unknown.
*/
CodeWriter owner;
/**
* Indicates if the position of this label is known.
*/
boolean resolved;
/**
* The position of this label in the code, if known.
*/
int position;
/**
* 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 CodeWriter#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 CodeWriter#visitMaxs visitMaxs}.
*/
Label next;
/**
* <tt>true</tt> if this basic block has been pushed in the basic block stack.
* See {@link CodeWriter#visitMaxs visitMaxs}.
*/
boolean pushed;
// --------------------------------------------------------------------------
// Constructor
// --------------------------------------------------------------------------
/**
* Constructs a new label.
*/
public Label () {
}
// --------------------------------------------------------------------------
// Methods to compute offsets and to manage forward references
// --------------------------------------------------------------------------
/**
* 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 CodeWriter owner,
final ByteVector out,
final int source,
final boolean wideOffset)
{
if (CodeWriter.CHECK) {
if (this.owner == null) {
this.owner = owner;
} else if (this.owner != owner) {
throw new IllegalArgumentException();
}
}
if (resolved) {
if (wideOffset) {
out.put4(position - source);
} else {
out.put2(position - source);
}
} else {
if (wideOffset) {
addReference(-1 - source, out.length);
out.put4(-1);
} else {
addReference(source, out.length);
out.put2(-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 CodeWriter#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 CodeWriter owner,
final int position,
final byte[] data)
{
if (CodeWriter.CHECK) {
if (this.owner == null) {
this.owner = owner;
}
if (resolved || this.owner != owner) {
throw new IllegalArgumentException();
}
}
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 CodeWriter). 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 <= Constants.JSR) {
// changes IFEQ ... JSR to opcodes 202 to 217 (inclusive)
data[reference - 1] = (byte)(opcode + 49);
} else {
// changes IFNULL and IFNONNULL to opcodes 218 and 219 (inclusive)
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;
}
}