RFR/RFC [8u]: Enable weak JNI handling with Shenandoah after JDK-8176100

[Aleksey Shipilev]

On 5/27/19 5:39 PM, Aleksey Shipilev wrote:
> On 5/27/19 3:29 PM, Roman Kennke wrote:
>> Looks like we've got a clash between rscratch1 used in
>> g1_write_barrier_pre() and the rscratch that's passed as tmp from
>> sharedRuntime_aarch64.cpp. You need this fix:
>>
>> diff -r 9f523f185755 src/cpu/aarch64/vm/sharedRuntime_aarch64.cpp
>> --- a/src/cpu/aarch64/vm/sharedRuntime_aarch64.cpp	Mon May 27 12:23:24
>> 2019 +0200
>> +++ b/src/cpu/aarch64/vm/sharedRuntime_aarch64.cpp	Mon May 27 09:27:22
>> 2019 -0400
>> @@ -2066,7 +2066,7 @@
>>        __ g1_write_barrier_pre(noreg /* obj */,
>>                                r0 /* pre_val */,
>>                                rthread /* thread */,
>> -                              rscratch1 /* tmp */,
>> +                              rscratch2 /* tmp */,
>>                                true /* tosca_live */,
>>                                true /* expand_call */);
>>      }
>>
>> This makes the failing test pass for me.
> 
> Yes, it does! Thank you.
> 
>> It probably warrants a more careful fix, extra asserts in
>> g1_write_barrier_pre() and checking if newer versions have similar problems.
> 
> This is apparently fixed by:
>   https://bugs.openjdk.java.net/browse/JDK-8186325
> 
> ...and we "just" need to backport it.

Here:
  https://mail.openjdk.java.net/pipermail/aarch64-port-dev/2019-May/007397.html

Assuming it is approved soon, we would need to wait for another 8u pull to get it.

-Aleksey