On Tue, 24 Oct 2023 19:49:17 GMT, Alan Bateman <al...@openjdk.org> wrote:
>> The result of `FindClass` is a local JNI handle (in
>> `find_class_from_class_loader`, called from `jni_FindClass` [1]). As such,
>> we need to wrap the return value of `FindClass` in a global reference when
>> storing it inside fallbackLinker.c.
>>
>> While investigating this, I also noticed an existing bug in
>> `JNIHandles::handle_type`. This method is used from the implementation of
>> `GetObjectRefType` ([2]), and from the implementation of `-Xcheck:jni` code.
>> The former specifies that `JNIInvalidRefType` is a valid return value, and
>> the latter compares the result against `JNIInvalidRefType`. However, if the
>> handle is not any valid type, the implementation bottoms out in a
>> `ShouldNotReachHere()`, meaning `JNIHandles::handle_type` can never return
>> `JNIInvalidRefType`. I've fixed this by letting the enclosing if/else chain
>> fall through to just returning the default result, which is
>> `JNIInvalidRefType`. In that case, I observe the expected stack trace when
>> running with `-Xcheck:jni`. For example:
>>
>>
>> FATAL ERROR in native method: Bad global or local ref passed to JNI
>> at
>> jdk.internal.foreign.abi.fallback.LibFallback.doDowncall(java.base@22-internal/Native
>> Method)
>> at
>> jdk.internal.foreign.abi.fallback.LibFallback.doDowncall(java.base@22-internal/LibFallback.java:94)
>> at
>> jdk.internal.foreign.abi.fallback.FallbackLinker.doDowncall(java.base@22-internal/FallbackLinker.java:197)
>> at
>> java.lang.invoke.LambdaForm$DMH/0x000001b585008000.invokeStaticInit(java.base@22-internal/LambdaForm$DMH)
>> at
>> java.lang.invoke.LambdaForm$MH/0x000001b585029400.invoke(java.base@22-internal/LambdaForm$MH)
>> at
>> java.lang.invoke.LambdaForm$MH/0x000001b58502d000.invokeExact_MT(java.base@22-internal/LambdaForm$MH)
>> at TestUpcallDeopt.payload(TestUpcallDeopt.java:93)
>> at TestUpcallDeopt.main(TestUpcallDeopt.java:84)
>> at
>> java.lang.invoke.LambdaForm$DMH/0x000001b585006800.invokeStatic(java.base@22-internal/LambdaForm$DMH)
>> at
>> java.lang.invoke.LambdaForm$MH/0x000001b58502a800.invoke(java.base@22-internal/LambdaForm$MH)
>> at
>> java.lang.invoke.Invokers$Holder.invokeExact_MT(java.base@22-internal/Invokers$Holder)
>> at
>> jdk.internal.reflect.DirectMethodHandleAccessor.invokeImpl(java.base@22-internal/DirectMethodHandleAccessor.java:154)
>> at
>> jdk.internal.reflect.DirectMethodHandleAccessor.invoke(java.base@22-internal/DirectMethodHandleAccessor.java:103)
>> at java.lang.reflect.Method.invo...
>
> src/java.base/share/native/libfallbackLinker/fallbackLinker.c line 48:
>
>> 46: Java_jdk_internal_foreign_abi_fallback_LibFallback_init(JNIEnv* env,
>> jclass cls) {
>> 47: (*env)->GetJavaVM(env, &VM);
>> 48: LibFallback_class = (*env)->NewGlobalRef(env, (*env)->FindClass(env,
>> "jdk/internal/foreign/abi/fallback/LibFallback"));
>
> It might be better to bail if FindClass returns null as there will be pending
> exception.
Good point. Will do
-------------
PR Review Comment: https://git.openjdk.org/jdk/pull/16349#discussion_r1370785574
