Weird VerifyError

Hi all,

I have the following problem. This is the sample code:

public class Demo {

    InnerClass i;
   
    Demo() {
        i = new InnerClass();
    }
   
    public static void main(String[] args) {
        Demo demo = new Demo();
    }
   
    class InnerClass {
    }
}

Without any instrumentation (of course) this code works. If I add my 
instrumentation, that basically logs the old value of variable 
assignements, I encounter a java.lang.VerifyError: Expecting to find 
object/array on stack. To give you an impression the resulting bytecode 
is attached. From a stack point of view imho the example should work. 
And indeed the example does work if I add the following changes:

public class Demo {
    public static void main(String[] args) {
        MyComponent comp = new MyComponent();
    }
}

public class MyComponent2 {
    InnerClass i;

    public MyComponent2() {
         i = new InnerClass();
    }

    static class InnerClass {}
}

The interesting point is, before I updated my Java Version from 6.10 to 
6.21 today, the second example also failed with exactly the same 
VerifyError message. So obviously the second case was considered a bug 
in the verifier. Attached you'll find the bytecode for my problem case. 
I highlighted the code area that the verifier doesn't seem to like ;-) 
Obviously the only case that doesn't work (in Java 6.21) is the case 
where everything is mashed up in the main class. I don't know if this is 
my error, or again a problem in the verifier. Btw. if I change the inner 
class to be static, the example works again. What do you guys think?

Best regards
Nikolas


// class version 50.0 (50)
// access flags 0x21
public class de/kl/uni/cs/nehmer/test2/Demo {

  // compiled from: Demo.java
  // access flags 0x0
  INNERCLASS de/kl/uni/cs/nehmer/test2/Demo$InnerClass de/kl/uni/cs/nehmer/test2/Demo InnerClass

  // access flags 0x0
  Lde/kl/uni/cs/nehmer/test2/Demo$InnerClass; i

  // access flags 0x0
  <init>()V
    TRYCATCHBLOCK L0 L1 L1 null
   L0
   L2
    INVOKESTATIC de/kl/uni/cs/nehmer/setup/log/Logger.methodCall ()V
    INVOKESTATIC de/kl/uni/cs/nehmer/setup/log/Logger.localVariableStart ()V
    LINENUMBER 7 L2
    ALOAD 0
    INVOKESPECIAL java/lang/Object.<init> ()V
   L3
   * LINENUMBER 8 L3
    ALOAD 0
    NEW de/kl/uni/cs/nehmer/test2/Demo$InnerClass
    DUP
    ALOAD 0
    INVOKESPECIAL de/kl/uni/cs/nehmer/test2/Demo$InnerClass.<init> (Lde/kl/uni/cs/nehmer/test2/Demo;)V
    SWAP
    DUP
    DUP
    GETFIELD de/kl/uni/cs/nehmer/test2/Demo.i : Lde/kl/uni/cs/nehmer/test2/Demo$InnerClass;
    LDC "i"
    INVOKESTATIC de/kl/uni/cs/nehmer/setup/log/Logger.logInstanceVariableAssignement (Ljava/lang/Object;Ljava/lang/Object;Ljava/lang/String;)V
    SWAP
    PUTFIELD de/kl/uni/cs/nehmer/test2/Demo.i : Lde/kl/uni/cs/nehmer/test2/Demo$InnerClass;*
   L4
    LINENUMBER 9 L4
    INVOKESTATIC de/kl/uni/cs/nehmer/setup/log/Logger.methodReturn ()V
    RETURN
   L1
    INVOKESTATIC de/kl/uni/cs/nehmer/setup/log/Logger.methodReturn ()V
    ATHROW
   L5
    LOCALVARIABLE this Lde/kl/uni/cs/nehmer/test2/Demo; L2 L5 0
    MAXSTACK = 4
    MAXLOCALS = 1

  // access flags 0x9
  public static main([Ljava/lang/String;)V
    TRYCATCHBLOCK L0 L1 L1 null
   L0
   L2
    INVOKESTATIC de/kl/uni/cs/nehmer/setup/log/Logger.methodCall ()V
    INVOKESTATIC de/kl/uni/cs/nehmer/setup/log/Logger.localVariableStart ()V
    LINENUMBER 13 L2
    NEW de/kl/uni/cs/nehmer/test2/Demo
    ACONST_NULL
    ASTORE 1
    DUP
    INVOKESPECIAL de/kl/uni/cs/nehmer/test2/Demo.<init> ()V
    INVOKESTATIC de/kl/uni/cs/nehmer/setup/log/Logger.getStackFrameCounter ()I
    INVOKESTATIC de/kl/uni/cs/nehmer/setup/log/Logger.getStackFrameActualityCounter ()I
    LDC 1
    ALOAD 1
    INVOKESTATIC de/kl/uni/cs/nehmer/setup/log/Logger.logLocalVariableAssignement (IIILjava/lang/Object;)V
    ASTORE 1
   L3
    INVOKESTATIC de/kl/uni/cs/nehmer/setup/log/Logger.localVariableStart ()V
    LINENUMBER 15 L3
    INVOKESTATIC de/kl/uni/cs/nehmer/setup/log/Logger.methodReturn ()V
    RETURN
   L1
    INVOKESTATIC de/kl/uni/cs/nehmer/setup/log/Logger.methodReturn ()V
    ATHROW
   L4
    LOCALVARIABLE args [Ljava/lang/String; L2 L4 0
    LOCALVARIABLE demo Lde/kl/uni/cs/nehmer/test2/Demo; L3 L4 1
    MAXSTACK = 2
    MAXLOCALS = 2
}
// class version 50.0 (50)
// access flags 0x20
class de/kl/uni/cs/nehmer/test2/Demo$InnerClass {

  // compiled from: Demo.java
  // access flags 0x0
  INNERCLASS de/kl/uni/cs/nehmer/test2/Demo$InnerClass de/kl/uni/cs/nehmer/test2/Demo InnerClass

  // access flags 0x1010
  final Lde/kl/uni/cs/nehmer/test2/Demo; this$0

  // access flags 0x0
  <init>(Lde/kl/uni/cs/nehmer/test2/Demo;)V
    TRYCATCHBLOCK L0 L1 L1 null
   L0
   L2
    INVOKESTATIC de/kl/uni/cs/nehmer/setup/log/Logger.methodCall ()V
    INVOKESTATIC de/kl/uni/cs/nehmer/setup/log/Logger.localVariableStart ()V
    LINENUMBER 17 L2
    ALOAD 0
    ALOAD 1
    SWAP
    DUP
    DUP
    GETFIELD de/kl/uni/cs/nehmer/test2/Demo$InnerClass.this$0 : Lde/kl/uni/cs/nehmer/test2/Demo;
    LDC "this$0"
    INVOKESTATIC de/kl/uni/cs/nehmer/setup/log/Logger.logInstanceVariableAssignement (Ljava/lang/Object;Ljava/lang/Object;Ljava/lang/String;)V
    SWAP
    PUTFIELD de/kl/uni/cs/nehmer/test2/Demo$InnerClass.this$0 : Lde/kl/uni/cs/nehmer/test2/Demo;
    ALOAD 0
    INVOKESPECIAL java/lang/Object.<init> ()V
    INVOKESTATIC de/kl/uni/cs/nehmer/setup/log/Logger.methodReturn ()V
    RETURN
   L1
    INVOKESTATIC de/kl/uni/cs/nehmer/setup/log/Logger.methodReturn ()V
    ATHROW
   L3
    LOCALVARIABLE this Lde/kl/uni/cs/nehmer/test2/Demo$InnerClass; L2 L3 0
    MAXSTACK = 2
    MAXLOCALS = 2
}

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