LookupSwitch

Hi!

 

I am trying to use LookupSwitch to transforming a previous created class
adding a new variable (“localPC”) and jump to specific locations in each
class method depending on “localPC”. The problem is that execution is not
going to where it should after LookupSwitch. Could anyone help me?

 

Here is the BCEL code (for simplicity, “localPC” is set to zero): 

 

Method[] methods = Repository.lookupClass(“MyClass”).getMethods();

ConstantPoolGen cp = new ConstantPoolGen(clazz.getConstantPool());

for(int i=1; i < methods.length; i++) {

    MethodGen mg = new MethodGen(methods[i], clazz.getClassName(), cp);

    InstructionList il = mg.getInstructionList();

    LocalVariableGen lg = mg.addLocalVariable("localPC", Type.INT, null,
null); 

    int index = lg.getIndex();

    …

    il.insert(new LOOKUPSWITCH(matchs, targets, defaultTarget));


    il.insert(new ILOAD(index));

    il.insert(new ISTORE(index));

    il.insert(new ICONST(0)); 

 

    mg.setMaxStack();

    mg.setMaxLocals();

    il.dispose();

}

 

The bytecode stays like this (using javap):

 

   0: iconst_0

   1: istore_2

   2: iload_2

   3: lookupswitch{ //7

            68: 68;

            69: 69;

            70: 70;

            71: 71;

            74: 74;

            75: 75;

            78: 78;

            default: 68 }

   68:      iconst_0  //other Variable

   69:      istore_1  //Other Variable

 

I got Verifier error and can’t understand what is wrong. Using JustIce
showed me that the execution is not going to where it should be after
lookupswitch and the stack is being empty after that…

 

VERIFIED_REJECTED

Constraint violated in method 'my_method()':

Instruction ISTORE constraint violated: Cannot consume 1 stack slots: only 0
slot(s) left on stack!

Stack:

Slots used: 0 MaxStack: 1.

 

InstructionHandle:   69: istore_1[60](1)

 

Execution Frame:

Local Variables:

0: MyClass

1: <unknown object>

2: int

OperandStack:

Slots used: 0 MaxStack: 1.

Execution flow:

   0: iconst_0    [InstructionContext]

   1: istore_2    [InstructionContext]

   2: iload_2     [InstructionContext]

   3: lookupswitch -> 68 ... [InstructionContext]

  69: istore_1    [InstructionContext]

 

Shouldn’t the execution go to 68 and not to 69!!!!!!???? I think that this
is the problem with the stack.

 

Thanks a lot,

 

Giovanni