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

[coleen.phillimore at oracle.com]

+1
Coleen

On 3/4/20 9:36 AM, Harold Seigel wrote:
> 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