[aarch64-port-dev ] Question about ISB usage in the aarch64 port

[Andrew Haley]

On 11/29/19 6:56 AM, Nick Gasson wrote:

> I don't think it helps on AArch64: that 
> OrderAccess::cross_modifying_fence() is only called when a thread is 
> about to return from the safepoint handler. But it's possible for a 
> safepoint with code patching to happen in the background while a thread 
> is in native code, in which case we still need to do an ISB when 
> returning to Java.

Indeed we do.

> I'm not sure how other ports that need a serialising instruction handle 
> this?

PPC requirements are very similar to ours. I would have thought they
already had something before this patch, or they would surely have had
some problems. In any case, I haven't studied the code transitions
that are covered by that this patch.

-- 
Andrew Haley  (he/him)
Java Platform Lead Engineer
Red Hat UK Ltd. <https://www.redhat.com>
https://keybase.io/andrewhaley
EAC8 43EB D3EF DB98 CC77 2FAD A5CD 6035 332F A671