On Wed, 10 Jul 2024 16:56:37 GMT, Volker Simonis <[email protected]> wrote:
>> src/java.instrument/share/classes/java/lang/instrument/ClassFileTransformer.java
>> line 179:
>>
>>> 177: * This means that a {@link LinkageError} triggered during
>>> transformation of
>>> 178: * {@code C} in a class {@code D} not directly related to {@code C}
>>> can repeatedly
>>> 179: * occur later in arbitrary user code which uses {@code D}.
>>
>> This paragraph looks okay but I can't help thinking we should have something
>> in normative text to reference that specifies the reentrancy behavior.
>> Maybe I missed it but I thought we have something in the API docs on this.
>
> I haven't found anything either. The only specification-relevant mentioning
> of the issue I found is in the [JVMTI
> Specification](https://docs.oracle.com/en/java/javase/21/docs/specs/jvmti.html#bci)
> referenced at the beginning of the PR:
>
>> Care must be taken to avoid perturbing dependencies, especially when
>> instrumenting core classes.
>
> The example that follows describes an infinite recursion when instrumenting
> the the `j.l.Object()` constructor.
>
> I think the exact reentrancy behavior isn't specified anywhere. Not even the
> exact that should be thrown in such a case is specified (see [8164165: JVM
> throws incorrect exception when ClassFileTransformer.transform() triggers
> class loading of class already being
> loaded](https://bugs.openjdk.org/browse/JDK-8164165) for a discussion of
> different scenarios).
>
> I think the real problem is that the JVMS predates the JVMTI specification
> and the interaction between instrumentation and class loading isn't clearly
> defined. I think it might even be possible to treat class loading errors
> during transformation differently, such that they will not lead to a
> permanent resolution error for the corresponding constant pool entries. I
> know that this will violate the current section ยง 5.4.3 Resolution
> (https://docs.oracle.com/javase/specs/jvms/se8/html/jvms-5.html#jvms-5.4.3)
> of the JVM specification which mandates that "if an attempt by the Java
> Virtual Machine to resolve a symbolic reference fails because an error is
> thrown that is an instance of LinkageError (or a subclass), then subsequent
> attempts to resolve the reference always fail with the same error that was
> thrown as a result of the initial resolution attempt". But as I wrote, that
> predates JVMTI and when JVMTI was added, we missed the opportunity to specify
> its exact impact on class loading
and resolution.
>
> But all this is a much bigger discussion. Maybe we should open another issue
> for it?
I've created [JDK-8336296)](https://bugs.openjdk.org/browse/JDK-8336296) for
the spec issues.
-------------
PR Review Comment: https://git.openjdk.org/jdk/pull/20011#discussion_r1675558673
