RFR (S): 8238460: Provide warnings about the use of JNI RegisterNatives to rebind native methods for boot/platform classes in other classloaders

[Lois Foltan]

On 2/4/2020 7:41 PM, David Holmes wrote:
> bug: https://bugs.openjdk.java.net/browse/JDK-8238460
> webrev: http://cr.openjdk.java.net/~dholmes/8238460/webrev/
>
> This small enhancement adds some usage warnings to the JNI 
> specification - see details in bug report - and a runtime warning in 
> the JNI RegisterNatives code, covering the case where platform native 
> methods get rebound by code that is not part of the platform. This is 
> needed by native agents, but may be unexpected in other contexts, 
> hence a warning is issued.
>
> A test is added to exercise the warning.
>
> Other testing: tiers 1-3
>
> The actual spec edit is not part of this RFR as the specs themselves 
> are not open-source.
>
> Thanks,
> David

Looks good, some minor comments:

prims/jni.cpp
- line #2931 - Consider calling 
SystemDictionary::is_platform_class_loader(cl) instead of manually 
comparing cl to SystemDictionary::java_platform_loader().
- line #2598 - Can you change to ResourceMark rm(THREAD)?  And while in 
this method, maybe the ResourceMark on line #2950 as well.

Thanks,
Lois