[Soot-list] Decoding CodeAttribute in the VM

[Sébastien]

Hi,

 

I do an analysis and I want to insert my result in a class file using a
CodeAttribute. Since I have some tags associate with some units, I use a
TagAggregator. 

 

In the following class, my analysis associates a tag with the instructions
<c4.toto = o> and <c41.tata = c4.toto>. Each tag has an one byte array
containing the value 0.

 

public class C4 {

            private Object toto;

            private Object tata;

            public static void main(String[] args) {

                        Object o = new Integer(4);

                        C4 c4 = new C4();

                        c4.toto = o;

                        C4 c41 = new C4();

                        c41.tata = c4.toto;

                        o = c41.tata;

            }

}

 

Here is my class file containing my new attribute. I used  ClassParser from
Apache to get this result. The tag aggregator associates each tag with the
putfield bytecode.

 

 

0:    new         <java.lang.Integer> (26)

3:    dup

4:    iconst_4

5:    invokespecial     java.lang.Integer.<init> (I)V (10)

8:    astore_0

9:    new         <C4> (16)

12:   dup

13:   invokespecial     C4.<init> ()V (17)

16:   dup

17:   aload_0

18:   putfield          C4.toto Ljava/lang/Object; (13)

21:   new         <C4> (16)

24:   dup

25:   invokespecial     C4.<init> ()V (17)

28:   astore_0

29:   getfield          C4.toto Ljava/lang/Object; (13)

32:   astore_1

33:   aload_0

34:   aload_1

35:   putfield          C4.tata Ljava/lang/Object; (27)

38:   aload_0

39:   getfield          C4.tata Ljava/lang/Object; (27)

42:   astore_0

43:   return

 

Attribute(s) = 

...

(Unknown attribute WriteBarrier: 00 02 00 12 00 00 23 00)

 

If I print each byte of my aggregated attribute data array, I get the
following:

0 2 0 18 0 0 35 0

 

So, I want to use this result in the VM.  The only thing I need is my 0
values. How can I decode (0 2 0 18 0 0 35 0) in the VM? I understand the
number 18 and 35 (the line number of the bytecode associated with my tag)
but where do come from 2 for example?

 

Thanks for your help


Séb

 

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