RFR: 8317545: AIX PPC64: Implementation of Foreign Function & Memory API [v2]

[Martin Doerr]

On Fri, 13 Oct 2023 14:28:58 GMT, Jorn Vernee <jvernee at openjdk.org> wrote:

>>> Just to clarify, is the ABI equal to what is described in this table: https://www.ibm.com/docs/en/xl-c-and-cpp-aix/16.1?topic=data-using-alignment-modes ?
>>> 
>>> This shows `double` having 8-byte alignment, but being 4-byte aligned when not the first member of an aggregate.
>> 
>> Interesting! This matches my understanding. I can see that doubles are 4-byte aligned within structures. The 8-byte alignment of the first member is already established by the allocation alignment.
>> 
>> I have only read the ABI documentation for linux. IBM will have to cover AIX specific details if there are more questions.
>
> Discussed this a bit with Maurizio. There are a few things to consider:
> 
> - `cannonicalLayouts` allows for just a single mapping from type name to layout. I think `double` should map to the 8-byte aligned layout. (the same alignment you get from `_Alignof(double)` in C).
> - We have to relax the checking done by the linker on AIX. Maybe change `AbstractLinker::checkLayoutRecursive` call some `checkStructMemberLayout` method, that by default just calls `checkLayoutRecursive`, but which the AIX linker can override to implement it's special rules for doubles.
> - We need a small spec update to allow for struct field layouts that are not canonical layouts. I'll take a stab at that, and then get back to you.

Thanks for your outstanding support! I'm awaiting feedback from IBM and a solution for the subtask https://bugs.openjdk.org/browse/JDK-8317799. There shouldn't be much work to be done after that, I guess.

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PR Review Comment: https://git.openjdk.org/jdk/pull/16179#discussion_r1358368099