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feilong is a suite of core and expanded libraries that include utility classes, http, excel,cvs, io classes, and much much more.
/*
* Javassist, a Java-bytecode translator toolkit.
* Copyright (C) 1999- Shigeru Chiba. 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,
* or the Apache License Version 2.0.
*
* 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 com.feilong.lib.javassist.bytecode;
/**
* Utility for computing max_stack.
*/
class CodeAnalyzer implements Opcode{
private ConstPool constPool;
private CodeAttribute codeAttr;
public CodeAnalyzer(CodeAttribute ca){
codeAttr = ca;
constPool = ca.getConstPool();
}
public int computeMaxStack() throws BadBytecode{
/*
* d = stack[i]
* d == 0: not visited
* d > 0: the depth is d - 1 after executing the bytecode at i.
* d < 0: not visited. the initial depth (before execution) is 1 - d.
*/
CodeIterator ci = codeAttr.iterator();
int length = ci.getCodeLength();
int[] stack = new int[length];
constPool = codeAttr.getConstPool();
initStack(stack, codeAttr);
boolean repeat;
do{
repeat = false;
for (int i = 0; i < length; ++i){
if (stack[i] < 0){
repeat = true;
visitBytecode(ci, stack, i);
}
}
}while (repeat);
int maxStack = 1;
for (int i = 0; i < length; ++i){
if (stack[i] > maxStack){
maxStack = stack[i];
}
}
return maxStack - 1; // the base is 1.
}
private void initStack(int[] stack,CodeAttribute ca){
stack[0] = -1;
ExceptionTable et = ca.getExceptionTable();
if (et != null){
int size = et.size();
for (int i = 0; i < size; ++i){
stack[et.handlerPc(i)] = -2; // an exception is on stack
}
}
}
private void visitBytecode(CodeIterator ci,int[] stack,int index) throws BadBytecode{
int codeLength = stack.length;
ci.move(index);
int stackDepth = -stack[index];
int[] jsrDepth = new int[1];
jsrDepth[0] = -1;
while (ci.hasNext()){
index = ci.next();
stack[index] = stackDepth;
int op = ci.byteAt(index);
stackDepth = visitInst(op, ci, index, stackDepth);
if (stackDepth < 1){
throw new BadBytecode("stack underflow at " + index);
}
if (processBranch(op, ci, index, codeLength, stack, stackDepth, jsrDepth)){
break;
}
if (isEnd(op)){
break;
}
if (op == JSR || op == JSR_W){
--stackDepth;
}
}
}
private boolean processBranch(int opcode,CodeIterator ci,int index,int codeLength,int[] stack,int stackDepth,int[] jsrDepth)
throws BadBytecode{
if ((IFEQ <= opcode && opcode <= IF_ACMPNE) || opcode == IFNULL || opcode == IFNONNULL){
int target = index + ci.s16bitAt(index + 1);
checkTarget(index, target, codeLength, stack, stackDepth);
}else{
int target, index2;
switch (opcode) {
case GOTO:
target = index + ci.s16bitAt(index + 1);
checkTarget(index, target, codeLength, stack, stackDepth);
return true;
case GOTO_W:
target = index + ci.s32bitAt(index + 1);
checkTarget(index, target, codeLength, stack, stackDepth);
return true;
case JSR:
case JSR_W:
if (opcode == JSR){
target = index + ci.s16bitAt(index + 1);
}else{
target = index + ci.s32bitAt(index + 1);
}
checkTarget(index, target, codeLength, stack, stackDepth);
/*
* It is unknown which RET comes back to this JSR.
* So we assume that if the stack depth at one JSR instruction
* is N, then it is also N at other JSRs and N - 1 at all RET
* instructions. Note that STACK_GROW[JSR] is 1 since it pushes
* a return address on the operand stack.
*/
if (jsrDepth[0] < 0){
jsrDepth[0] = stackDepth;
return false;
}else if (stackDepth == jsrDepth[0]){
return false;
}else{
throw new BadBytecode("sorry, cannot compute this data flow due to JSR: " + stackDepth + "," + jsrDepth[0]);
}
case RET:
if (jsrDepth[0] < 0){
jsrDepth[0] = stackDepth + 1;
return false;
}else if (stackDepth + 1 == jsrDepth[0]){
return true;
}else{
throw new BadBytecode("sorry, cannot compute this data flow due to RET: " + stackDepth + "," + jsrDepth[0]);
}
case LOOKUPSWITCH:
case TABLESWITCH:
index2 = (index & ~3) + 4;
target = index + ci.s32bitAt(index2);
checkTarget(index, target, codeLength, stack, stackDepth);
if (opcode == LOOKUPSWITCH){
int npairs = ci.s32bitAt(index2 + 4);
index2 += 12;
for (int i = 0; i < npairs; ++i){
target = index + ci.s32bitAt(index2);
checkTarget(index, target, codeLength, stack, stackDepth);
index2 += 8;
}
}else{
int low = ci.s32bitAt(index2 + 4);
int high = ci.s32bitAt(index2 + 8);
int n = high - low + 1;
index2 += 12;
for (int i = 0; i < n; ++i){
target = index + ci.s32bitAt(index2);
checkTarget(index, target, codeLength, stack, stackDepth);
index2 += 4;
}
}
return true; // always branch.
}
}
return false; // may not branch.
}
private void checkTarget(int opIndex,int target,int codeLength,int[] stack,int stackDepth) throws BadBytecode{
if (target < 0 || codeLength <= target){
throw new BadBytecode("bad branch offset at " + opIndex);
}
int d = stack[target];
if (d == 0){
stack[target] = -stackDepth;
}else if (d != stackDepth && d != -stackDepth){
throw new BadBytecode("verification error (" + stackDepth + "," + d + ") at " + opIndex);
}
}
private static boolean isEnd(int opcode){
return (IRETURN <= opcode && opcode <= RETURN) || opcode == ATHROW;
}
/**
* Visits an instruction.
*/
private int visitInst(int op,CodeIterator ci,int index,int stack) throws BadBytecode{
String desc;
switch (op) {
case GETFIELD:
stack += getFieldSize(ci, index) - 1;
break;
case PUTFIELD:
stack -= getFieldSize(ci, index) + 1;
break;
case GETSTATIC:
stack += getFieldSize(ci, index);
break;
case PUTSTATIC:
stack -= getFieldSize(ci, index);
break;
case INVOKEVIRTUAL:
case INVOKESPECIAL:
desc = constPool.getMethodrefType(ci.u16bitAt(index + 1));
stack += Descriptor.dataSize(desc) - 1;
break;
case INVOKESTATIC:
desc = constPool.getMethodrefType(ci.u16bitAt(index + 1));
stack += Descriptor.dataSize(desc);
break;
case INVOKEINTERFACE:
desc = constPool.getInterfaceMethodrefType(ci.u16bitAt(index + 1));
stack += Descriptor.dataSize(desc) - 1;
break;
case INVOKEDYNAMIC:
desc = constPool.getInvokeDynamicType(ci.u16bitAt(index + 1));
stack += Descriptor.dataSize(desc); // assume CosntPool#REF_invokeStatic
break;
case ATHROW:
stack = 1; // the stack becomes empty (1 means no values).
break;
case MULTIANEWARRAY:
stack += 1 - ci.byteAt(index + 3);
break;
case WIDE:
op = ci.byteAt(index + 1);
// don't break here.
default:
stack += STACK_GROW[op];
}
return stack;
}
private int getFieldSize(CodeIterator ci,int index){
String desc = constPool.getFieldrefType(ci.u16bitAt(index + 1));
return Descriptor.dataSize(desc);
}
}