Dear ARM32 Maintainers, Boris, Sergey, [1]

ARM32 does not implement nmethod entry barriers (see 
https://bugs.openjdk.org/browse/JDK-8291302).

This is actually a defect because nmethod entry barriers are a G1 requirement 
where they are needed during concurrent marking to keep alive nmethod oop 
constants as they are all weak oops[2].

I'd like to do a clean-up which removes redundant stackwalks from the G1 remark 
pause[3]. With nmethod entry barriers they are not necessary as they do the 
same keep alive for oop constants of nmethods found on stack. Without nmethod 
barriers (ARM32) these stackwalks are not sufficient though as every nmethod 
that is called during concurrent marking needs to do the keep alive for SATB.

Could you share your plans regarding the implementation of nmethod entry 
barriers? How would you like me to handle ARM32 in the intended clean-up?

Thanks,
Richard.

[1] found you on https://wiki.openjdk.org/display/HotSpot/Ports
[2] https://bugs.openjdk.org/browse/JDK-8288970
[3] https://github.com/openjdk/jdk/pull/11314

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