Re: Re: Re: IllegalStateException: Try catch blocks must be visited before their labels

Hi,

Can anybody comment on this? 


Thanks.

---- On Mon, 31 Jan 2011 19:43:31 +0530 Rajaraman Santhanam <[email protected]> wrote ---- 

Hi Tronje,

What you say makes sense. Either VM is a bit lenient or CheckClassAdaptor is strict.


I tried with a simple java file and this seems to be the behavior. I get the issue only when I keep CheckClassAdapter in front of my visitors.
MyClassAdapter adapter =  new MyClassAdapter(new CheckClassAdapter(writer), className, classBeingRedefined); 



Also I found that, if I run the CheckClassAdapter(as below) after bytecode transformation I don't see any issue at all.
StringWriter checkClassSW = new StringWriter();
PrintWriter checkClassPW = new PrintWriter(checkClassSW);
CheckClassAdapter.verify(reader, loader, dump, checkClassPW);
System.out.println(checkClassSW.toString());
try
{
            checkClassPW.close();
            checkClassSW.close();
}
catch(Exception ex)
{
            ex.printStackTrace();
} 


It looks like CheckClassAdaptor looks for some state and it finds visitLabel called before trycatchblock. However the same adaptor behaves differently :-( 

Also attaching the sources I used for testing.


Thanks,
Rajaraman




---- On Sat, 29 Jan 2011 21:15:52 +0530 Tronje Krop <[email protected]> wrote ---- 

Hi Rajaraman, 
 
it is as the error says. You have instrumented the byte-code in a way 
that at least one of the labels has been visited before defining the 
try-catch-block. The CheckMethodAdapter checks this requirement and 
throws the exception. 
 
If you are right with your claim, it seems that the VM-Verifier has a 
relaxed condition which allows to define the try-catch-block using labels 
have being visited before. 
 
I didn't find a rule in the VM-specification that prohibits this, but 
I have not looked very close. Therefore, I think the CheckClassAdapter 
may be to restrictive unless ASM has a problem with this relaxed 
condition. 
 
I think we must investigate this issue closer. 
 
CU Tronje 
 
 
Rajaraman Santhanam wrote: 
> Hi, 
> 
> I get this exception if I put CheckClassAdapter in the visitors chain before ClassWriter. The code I use is below: 
> ClassReader reader = new ClassReader(classfileBuffer); 
> ClassWriter writer = new ClassWriter(reader, ClassWriter.COMPUTE_MAXS); 
> 
> 
> BasicClassAdapter adapter = new BasicClassAdapter(new CheckClassAdapter(writer), className, classBeingRedefined); 
> reader.accept(adapter, ClassReader.SKIP_DEBUG); 
> 
> By running this I get error with details: 
> java.lang.IllegalStateException: Try catch blocks must be visited before their labels 
> at org.objectweb.asm.util.CheckMethodAdapter.visitTryCatchBlock(CheckMethodAdapter.java:679) 
> at org.objectweb.asm.MethodAdapter.visitTryCatchBlock(MethodAdapter.java:170) 
> at test.agent.instrumentation.BasicMethodAdapter.visitMaxs(BasicMethodAdapter.java:86) 
> 
> However my instrumentation code work perfectly well if run this without CheckClassAdapter. Not sure what I'm missing here. 
> 
> 
> I tried this when seeing the mail from Eugene to use CheckClassAdapter to catch various issues. 
> 
> 
> My BasicClassAdapter is the implementation of FinallyAdapter from asm-transformations.pdf 
> 
> 
> Can somebody help me out here? 
> 
> 
> Regards, 
> Rajaraman 
> 
> 
> 
> 
 
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