[aarch64-port-dev ] Webrev of Oracle ARM & AARCH64 Sources

[Andrew Haley]

On 29/09/16 11:54, Andrey Petushkov wrote:
> 
>> On 29 Sep 2016, at 13:43, Andrew Haley <aph at redhat.com> wrote:
>>
>> On 29/09/16 11:13, Andrey Petushkov wrote:
>>
>>> In addition, aarch32 port shares much in common with RH’s aarch64
>>> implementation so well, if you keep aarch64 in main openjdk repos
>>> it’s much easier to merge aarch32 into it, rather than merge with
>>> Sun/Oracle’s arm implementation.
>>
>> There is no good technical reason for AArch64 to merge with AArch32,
>> and IMO it would create a mess.  AArch64 is a clean-sheet design which
>> shares some of its DNA with AArch32, but that is all.  It's not like
>> x86-64, which is a 64-bit extension of x86.
>
> Well, it’s AArch32 which is not clean-sheet design but rather
> borrows from AArch64 :)

I meant to say: the AArch64 hardware architecture is a clean-sheet
design which shares some of its DNA with AArch32, but that is all.

> I admit that there are much more difference between architectures
> than for x86 so you might be right that the difference in the code
> could be too big. I just have a feeling it’s not. I can mistake of
> course, I did not diff specifically

Possibly.  I don't really want to make the port a mess of #ifdefs and
suchlike, so I'd fight pretty hard against it.

It is possible to do some macro trickery to write common runtime
routines, but with sufficient such trickery it'd be possible to do
that with any two unrelated arches.  While it might save some time, it
adds another layer of complexity and makes it harder to write
efficient and idiomatic code.  In particular things such as predicated
instructions, which are an important part of the AArch32 ISA, are
absent on AArch64.

Andrew.