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/*
* Javassist, a Java-bytecode translator toolkit.
* Copyright (C) 1999-2007 Shigeru Chiba, and others. All Rights Reserved.
*
* The contents of this file are subject to the Mozilla Public License Version
* 1.1 (the "License"); you may not use this file except in compliance with
* the License. Alternatively, the contents of this file may be used under
* the terms of the GNU Lesser General Public License Version 2.1 or later.
*
* Software distributed under the License is distributed on an "AS IS" basis,
* WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
* for the specific language governing rights and limitations under the
* License.
*/
package javassist.bytecode.analysis;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Map;
import java.util.Set;
import javassist.bytecode.BadBytecode;
import javassist.bytecode.CodeAttribute;
import javassist.bytecode.CodeIterator;
import javassist.bytecode.ExceptionTable;
import javassist.bytecode.MethodInfo;
import javassist.bytecode.Opcode;
/**
* Discovers the subroutines in a method, and tracks all callers.
*
* @author Jason T. Greene
*/
public class SubroutineScanner implements Opcode {
private Subroutine[] subroutines;
Map subTable = new HashMap();
Set done = new HashSet();
public Subroutine[] scan(MethodInfo method) throws BadBytecode {
CodeAttribute code = method.getCodeAttribute();
CodeIterator iter = code.iterator();
subroutines = new Subroutine[code.getCodeLength()];
subTable.clear();
done.clear();
scan(0, iter, null);
ExceptionTable exceptions = code.getExceptionTable();
for (int i = 0; i < exceptions.size(); i++) {
int handler = exceptions.handlerPc(i);
// If an exception is thrown in subroutine, the handler
// is part of the same subroutine.
scan(handler, iter, subroutines[exceptions.startPc(i)]);
}
return subroutines;
}
private void scan(int pos, CodeIterator iter, Subroutine sub) throws BadBytecode {
// Skip already processed blocks
if (done.contains(Integer.valueOf(pos)))
return;
done.add(Integer.valueOf(pos));
int old = iter.lookAhead();
iter.move(pos);
boolean next;
do {
pos = iter.next();
next = scanOp(pos, iter, sub) && iter.hasNext();
} while (next);
iter.move(old);
}
private boolean scanOp(int pos, CodeIterator iter, Subroutine sub) throws BadBytecode {
subroutines[pos] = sub;
int opcode = iter.byteAt(pos);
if (opcode == TABLESWITCH) {
scanTableSwitch(pos, iter, sub);
return false;
}
if (opcode == LOOKUPSWITCH) {
scanLookupSwitch(pos, iter, sub);
return false;
}
// All forms of return and throw end current code flow
if (Util.isReturn(opcode) || opcode == RET || opcode == ATHROW)
return false;
if (Util.isJumpInstruction(opcode)) {
int target = Util.getJumpTarget(pos, iter);
if (opcode == JSR || opcode == JSR_W) {
Subroutine s = (Subroutine) subTable.get(Integer.valueOf(target));
if (s == null) {
s = new Subroutine(target, pos);
subTable.put(Integer.valueOf(target), s);
scan(target, iter, s);
} else {
s.addCaller(pos);
}
} else {
scan(target, iter, sub);
// GOTO ends current code flow
if (Util.isGoto(opcode))
return false;
}
}
return true;
}
private void scanLookupSwitch(int pos, CodeIterator iter, Subroutine sub) throws BadBytecode {
int index = (pos & ~3) + 4;
// default
scan(pos + iter.s32bitAt(index), iter, sub);
int npairs = iter.s32bitAt(index += 4);
int end = npairs * 8 + (index += 4);
// skip "match"
for (index += 4; index < end; index += 8) {
int target = iter.s32bitAt(index) + pos;
scan(target, iter, sub);
}
}
private void scanTableSwitch(int pos, CodeIterator iter, Subroutine sub) throws BadBytecode {
// Skip 4 byte alignment padding
int index = (pos & ~3) + 4;
// default
scan(pos + iter.s32bitAt(index), iter, sub);
int low = iter.s32bitAt(index += 4);
int high = iter.s32bitAt(index += 4);
int end = (high - low + 1) * 4 + (index += 4);
// Offset table
for (; index < end; index += 4) {
int target = iter.s32bitAt(index) + pos;
scan(target, iter, sub);
}
}
}
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