[External] : Re: Verification in agent transformers

[Ryan Ernst]

I created a reproduction:

https://github.com/rjernst/verify-error-repro
rjernst/verify-error-repro
github.com

Again, the VerifyError is correct, it’s what we expect (we created bad bytecode in a transform), but it doesn’t always occur.


> On Mar 8, 2025, at 12:55 AM, Alan Bateman <Alan.Bateman at oracle.com> wrote:
> 
> 
> 
> 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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