[14u] RFR 8237632: Shenandoah: accept NULL fwdptr to cooperate with JVMTI and JFR

[Zhengyu Gu]

On 3/2/20 10:54 AM, Zhengyu Gu wrote:
> Hi,
> 
> I would like to backport this patch to 14u.
> 
> Shenandoah and JVMTI/JFR leakprofiler all use object mark word's 
> 'marked' pattern, but for different purpose. Without this patch, it can 
> result fatal crash for Shenandoah, as it interpreters JVMTI/JFR visited 
> objects as forwarding objects.
> 
> The original patch does not apply cleanly, mainly due to line shifts and 
> missing JDK-8236888 in JDK14u.

Sorry, wrong bug Id, JDK-8236888 -> JDK-8237963.

-Zhengyu


> 
> Original bug: https://bugs.openjdk.java.net/browse/JDK-8237632
> Original code review: 
> https://mail.openjdk.java.net/pipermail/hotspot-gc-dev/2020-February/028693.html 
> 
> 
> 14u Webrev: http://cr.openjdk.java.net/~zgu/JDK-8237632/14u/webrev.00/
> 
> 
> Test:
>    hotspot_gc_shenandoah
>    vmTestbase_nsk_jvmti
>    vmTestbase_nsk_jdi
> 
> Thanks,
> 
> -Zhengyu
>