[External] : Re: Verification in agent transformers

[Alan Bateman]

On 07/03/2025 23:50, Ryan Ernst wrote:
> > If the class is loaded and then linked, and is not on the bootstrap 
> class loader, then it should be verified.
>
> I agree, but that’s not what we observed. We only see the VerifyError 
> if retransformClasses is called. If instead the class is loaded after 
> the transformer has been registered, no VerifyError occurs, even 
> though the transformer produced technically broken bytecode (I say 
> “technically” because although the parameter type was wrong, we never 
> used the parameter in this method, so it didn’t actually cause any 
> problems at runtime, it was just a bad reference on the stack that was 
> ignored).

I think the question you are asking is whether there is verification of 
classes modified at class load time with a ClassFileTransformer 
(ClassFileLoadHook in JVMTI speak) when those classes are in modules 
mapped to the boot class loader.

-Alan
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