arm32 status

[Peter Johnson]

On Tue, Feb 2, 2021 at 8:04 AM Aleksey Shipilev <shade at redhat.com> wrote:
> On 2/2/21 4:53 PM, Peter Johnson wrote:
> > Is anyone actively working on arm32 support?  The wiki says "in
> > development, help wanted" and Aleksey’s Sept 2019 presentation says
> > "prototyping," but it doesn’t appear like there’s anything committed in
> > hotspot/cpu/arm/gc. Does anyone have a work in progress on a personal fork?
>
> I had started it at pre-COVID times, but then we had to stabilize ARM32 itself. Once we reached some
> level of ARM32 stability, other things preempted further ARM32 work. I have restarted the ARM32 port
> work yesterday, but -- kid you not -- I have to stabilize ARM32 itself before continuing! Such is life.
>
> So the bird-eye-view status is: the port is not even in alpha stage.
>
> What is your interest? Are you willing to contribute the port? :)

I'm willing to help, but I'm worried that taking on the full
implementation is a bit too much of a hill for me to climb in a
reasonable timeframe (particularly if ARM32 itself is unstable!).
I've worked before at this level in x86 assembly, but not in ARM, and
I've not worked on the JDK codebase before.  In reviewing the aarch64
implementation, it looks like the barrierSetAssembler is the critical
component?  In comparing other barrierSetAssembler implementations
between aarch64 and arm, there is significant similarity but also
non-obvious (to me) differences, so I'd be worried about missing
something fundamental when porting Shenandoah.

-- 
Thanks,
-Peter