RFR: 8368182: AOT cache creation fails with class defined by JNI

[David Holmes]

On Tue, 23 Sep 2025 04:12:38 GMT, Ioi Lam <iklam at openjdk.org> wrote:

>> src/hotspot/share/classfile/classLoader.cpp line 1196:
>> 
>>> 1194:   if (src == nullptr) {
>>> 1195:     if (loader == nullptr) {
>>> 1196:       // JFR classes
>> 
>> What was this referring to? I traced this back to "8186842: Use Java class loaders for creating the CDS archive" but no mention of any JFR classes was made. FWIW I can't see any use of JNI DefineClass in the JDK code, so this change would only affect end-user code.
>
> JFR doesn't call JNI DefineClass. Instead, it uses `ClassFileStream` and `ClassFileParser` directly, so it can accomplish the same thing (defining a class with a NULL code source).
> 
> The above was written when JFR was defining classes with a with a NULL code source:
> 
> https://github.com/openjdk/jdk/blob/02f895c5f6f6de38549337d45ed8ba4c446e9677/src/hotspot/share/jfr/instrumentation/jfrEventClassTransformer.cpp#L1165
> 
> JFR has since been updated to pass a non-null code source to `ClassFileStream`, so the comment about JFR classes is no longer valid.

Thanks for clarifying.

>> test/hotspot/jtreg/runtime/cds/appcds/aotCache/libJNIDefineClassApp.c line 34:
>> 
>>> 32:     jclass returnValue = (*env)->DefineClass(env, classNameChar, classLoader, arrayContent, bytecodeLength);
>>> 33:     (*env)->ReleaseByteArrayElements(env, bytecode, arrayContent, JNI_ABORT);
>>> 34:     (*env)->ReleaseStringUTFChars(env, className, classNameChar);
>> 
>> Does this pass `-Xcheck:jni`? ie. do you need to check for exceptions in the above sequence.
>
> I copied the code from here. Is this style OK for jtreg tests?
> 
> https://github.com/openjdk/jdk/blob/61c5245bf7d6626b0c816612adcb0d94d6863644/test/hotspot/jtreg/vmTestbase/gc/g1/unloading/libdefine.cpp#L44-L52

I don't know if that one passes `-Xcheck:jni` either (I think we only run runtime tests with `-Xcheck:jni`), so please check else it may fail in tier4. Thanks

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PR Review Comment: https://git.openjdk.org/jdk/pull/27412#discussion_r2371294521
PR Review Comment: https://git.openjdk.org/jdk/pull/27412#discussion_r2371297714