[8u] RFR: JDK-8253036: Support building the Zero assembler port on AArch64

[Volker Simonis]

On Sat, Nov 21, 2020 at 11:04 AM Andrew Haley <aph at redhat.com> wrote:
>
> On 11/20/20 8:01 PM, Volker Simonis wrote:
>
> > In another private mail you were mentioning that the aarch64 port
> > which is intended for integration into 8u-dev will be based on
> > IcedTea's HotSpot at 8u272 and is targeted for 8u282 in January. The
> > Corretto team is very interested in having  the aarch64 port in 8u-dev
> > and we want to offer some assistance if you think that could help? Do
> > you already have a JBS issue to track this work?
> >
> > We are also interested in which compiler you will be using for
> > building the aarch64 in 8u? We are currently building with GCC 7 but
> > that still produces quite some warnings in shared code so we are
> > interested in downporting changes from higher jdk versions which fix
> > these warnings. This is even more important as we plan to move to gcc
> > 10 eventually because that has support for the new ARM outline atomics
> > [1] but that requires even more warning fixes. Using outline atomics
> > in compiled code showed nice performance improvements in our
> > benchmark results for some GC-heavy workloads.
>
> I would be extremely sceptical about "fixing warnings" in a backport.
> There has been a long and sorry history of warning fixes breaking
> release code, and many warnings are bogus.
>
> Unless a warning reveals a real bug or risky code, the code shouldn't be
> changed.

Unfortunately, for a "relatively new" platform like aarch64 we'll have
to use a "newer" compiler if we want to make full use of its features
(see [1] for example).

As long as the new compiler is just emitting additional warnings, we
can still build by ignoring the warnings (although that's not nice
either). If the newer compiler has turned warnings into errors,
there's no other way than fixing the code and if these fixes have
already been done in a later version I'd rather downport them instead
of fixing them manually in 8u.

All that said, I'd actually only wanted to know:
 - what's the current status of the aarch64 port integration into 8u
 - what gcc version you are targeting for that integration
 - how we can help with both, the integration as well as a potential
move to a newer compiler

As far as I can read in JDK-8144695 [2], Severin is experimenting with
gcc 10 for 8u as well. So maybe we don't even need that many overall
changes in order to make it work?

Best regards,
Volker

[1] https://community.arm.com/developer/tools-software/tools/b/tools-software-ides-blog/posts/making-the-most-of-the-arm-architecture-in-gcc-10
[2] https://bugs.openjdk.java.net/browse/JDK-8144695

>
> --
> 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
>