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

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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