ARM port consolidation

[Gil Tene]

This makes sense to me on the Aarch64 side.

However, on the ARM32 side, I don't think the situation is as straightforward as
what is being presented below, and I think more discussion and exploration of
alternatives is needed.

Much like with AArch64, there is an existing, active, community-developed and
community-supported AArch32 port in OpenJDK that predates Oracle's open
sourcing of their ARM32 version. That port is being used by multiple downstream
builds and, at least for the past year+, it seems to have had more attention and
ongoing engineering commitment around it than the Oracle variant.

Before making a choice of one AArch32 port vs the other (if such a choice
even needs to be made), I would like to hear more about the resources being
committed towards maintaining each, keeping each up to date, testing them on
various platforms (e.g. including building, testing, and supporting the popular
softfloat ABI variants imposed by some OS packages) and working on bug
fixes as needs appear.

— Gil.

> On Jun 4, 2018, at 6:24 PM, David Holmes <david.holmes at oracle.com> wrote:
> 
> Hi Bob,
> 
> Looping in porters-dev, aarch32-port-dev and aarch64-port-dev.
> 
> I think this is a good idea.
> 
> Thanks,
> David
> 
> On 5/06/2018 6:34 AM, Bob Vandette wrote:
>> During the JDK 9 time frame, Oracle open sourced its 32-bit and 64-bit
>> ARM ports and contributed them to OpenJDK.  These ports have been used for
>> years in the embedded and mobile market, making them very stable and
>> having the benefit of a single source base which can produce both 32 and
>> 64-bit binaries.  The downside of this contribution is that it resulted
>> in two 64-bit ARM implementations being available in OpenJDK.
>> I'd like to propose that we eliminate one of the 64-bit ARM ports and
>> encourage everyone to enhance and support the remaining 32 and 64 bit
>> ARM ports. This would avoid the creation of yet another port for these chip
>> architectures.  The reduction of competing ports will allow everyone
>> to focus their attention on a single 64-bit port rather than diluting
>> our efforts.  This will result in a higher quality and a more performant
>> implementation.
>> The community at large (especially RedHat, BellSoft, Linaro and Cavium)
>> have done a great job of enhancing and keeping the AArch64 port up to
>> date with current and new Hotspot features.  As a result, I propose that
>> we standardize the 64-bit ARM implementation on this port.
>> If there are no objections, I will file a JEP to remove the 64-bit ARM
>> port sources that reside in jdk/open/src/hotspot/src/cpu/arm
>> along with any build logic.  This will leave the Oracle contributed
>> 32-bit ARM port and the AArch64 64-bit ARM port.
>> Let me know what you all think,
>> Bob Vandette