Hi Andrew
Thank you for recommending me the VM spec...
But my prob is a little different,
as you have said I can add local variables using
LocalVar var = localvargen.addLocalvar()
int index = var.getIndex();
llcalvargen.setstart( ilist.append ( new ASTORE ( index ) ) )
.
.
.
as many as required
and at the calling setMaxLocals();
That is OK.
but now consider a scenario like this
public int getI(){
return 2;
}
Now I am trying to insert try-finally to this method by
instrumenting in bytecode
which should look like
public int getI(){
try{
return 2;
}finally {
System.out.println("sample");
}
}
To create this, I should create a empty catch block which throws
the exception that is not handled and redirect all the calls to finally
before the
return statement
now comes the problem with local variables.
I will get the instructionlist
I will find the instance of return, and insert a JSR instr
before this return and redirect all the branches
Next step is creation of catch block, where I have a problem
here I should store the exception, make a jsr
call, load the exception which I stored before and rethrow it
so I use ilist.append ( new ASTORE ( ? ) )
ilist.append ( new JSR() );
ilist.load ( new ALOAD ( ? ) )
so what should I use in the place of "?" (2,3,4......)
same while creating finally block, I should store the return
address
ilist.append ( new ASTORE ( ?? ) )
// performs the instrumentation of system.out.....
ret ??
so what should I use in place of "?" (2,3,4......)
so what I am doing is
getting the max_index (maximum index) available in the
localvargen
and assigning max_index+1 to the first ?
and assigning max_index+2 to the second ??
am I wrong in doing like these?????
is there some other efficient way for doing this???
Please help me in this regard.
Thank you
Reddy
>-----Original Message-----
>From: Andrew Huntwork [mailto:[EMAIL PROTECTED]
>Sent: Dienstag, 8. Februar 2005 16:01
>To: BCEL Users List
>Subject: Re: Query regarding index of local variables
>
>
>First, let me recommend a book to you that you may already know about:
>http://java.sun.com/docs/books/vmspec/2nd-edition/html/VMSpecTO
>C.doc.html
>
>read carefully enough, this book will tell you everything you need to
>know to screw around with class files to your heart's content.
>
>see below.
>
>Koduru, Rajendra Kumar Reddy wrote:
>[...]
>> // code
>>
>> int i = methodgen.getLocalVariables().length
>> my_lv1 = i+1;
>> my_lv2 = i+2;
>> my_lv = i+3;
>>
>> // code
>>
>> and I used to store using il.append ( new ASTORE ( my_lv2 ) );
>>
>>
>> I encountered a problem with this, i.e. the variable i returned
>> 22,
>> where as the max index is 7.. So there was overlap in the local
>> vars and my class file got corrupted
>
>there is no relationship between number of local variables and
>the first
>free slot. each LocalVariable describes the type contained in a slot
>over a particular range of instructions. there are 0 or more
>LocalVariables for each slot. You should print out the various fields
>in your LocalVariables just to get a feel for what they contain,
>especially the start index, end index and type.
>
>what you want is:
>
>setMaxLocals(); //if you have inserted variables already
>int i = methodgen.getMaxLocals();
>...
>
>In the project I used to work on (sandmark.cs.arizona.edu),
>almost every
>occurrence of getLocalVariables was a bug. That's because the local
>variable table may be incomplete, inaccurate (to some extent),
>obfuscated, or just plain missing (MethodGen.removeLocalVariables() or
>something like that).
>
>>
>>
>>
>> I just wanted to know..why is it like that.. Doesn't each local
>> variable have unique index?
>>
>> Isnt the length (i that is returned) mean the no of local
>> variables in the corresponding method?
>>
>> However now I tried using
>>
>> // code
>>
>> int max_index = 0;
>>
>> LocalVariableGen[] lv1 = mgen.getLocalVariables();
>>
>> for(int i = 0; i< lv1.length; i++){
>>
>> if(lv1[i].getIndex() > max_index)
>> max_index = lv1[i].getIndex();
>> }
>>
>> my_lv1 = i+1;
>> my_lv2 = i+2;
>> my_lv = i+3;
>>
>> // code
>>
>> and it works fine..
>>
>> but I just wanted to clarify it.
>>
>> Please help me in this regard.
>>
>>
>> Thank you
>> Reddy
>>
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>>
>
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