RFR: 8240529: CheckUnhandledOops breaks NULL check in Modules::define_module

[Harold Seigel]

Looks good and trivial.  Thanks for finding and fixing this.

Harold

On 3/4/2020 9:25 AM, Stefan Karlsson wrote:
> Hi all,
>
> Please review this small fix to CheckUnhandledOops.
>
> https://cr.openjdk.java.net/~stefank/8240529/webrev.01
> https://bugs.openjdk.java.net/browse/JDK-8240529
>
> 'loader' is an unhandled oop that is alive across a safepoint check 
> and then is used for a NULL check. When the safepoint check executes 
> the value of the oop is changed to 0xff...ff1. If the oop was NULL 
> then the check now starts to fail. When this happens 
> ClassLoader::_exploded_entries isn't populated as expected, causing 
> class loading failures with exploded builds.
>
> Thanks,
> StefanK