RFR: 8314949: linux PPC64 Big Endian: Implementation of Foreign Function & Memory API

[Maurizio Cimadamore]

On Thu, 24 Aug 2023 13:56:12 GMT, Martin Doerr <mdoerr at openjdk.org> wrote:

> I've found a way to solve the remaining FFI problem on linux PPC64 Big Endian. Large structs (>8 Bytes) which are passed in registers or on stack require shifting the Bytes in the last slot if the size is not a multiple of 8. This PR adds the required functionality to the Java code.
> 
> Please review and provide feedback. There may be better ways to implement it. I just found one which works and makes the tests pass:
> 
> Test summary
> ==============================
>    TEST                                              TOTAL  PASS  FAIL ERROR   
>    jtreg:test/jdk/java/foreign                          88    88     0     0   
> 
> 
> Note: This PR should be considered as preparation work for AIX which also uses ABIv1.

Overall these changes look good - as commented I'd like to learn a bit more of the underlying ABI, to get a sense of whether adding a new binding is ok. But overall it's great to see support for a big-endian ABI - apart from the linker, I am pleased to see that you did not encounter too many issues in the memory-side of the FFM API.

src/java.base/share/classes/jdk/internal/foreign/abi/Binding.java line 695:

> 693:      *   Negative [shiftAmount] shifts right and converts to int if needed.
> 694:      */
> 695:     record ShiftLeft(int shiftAmount, Class<?> type) implements Binding {

Given the situation you are facing, perhaps adding the new binding here is unavoidable. Let's wait to hear from @JornVernee. In the meantime, can you point me to a document which explains this behavior? I'm curious and I'd like to know more :-)

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PR Review: https://git.openjdk.org/jdk/pull/15417#pullrequestreview-1594603192
PR Review Comment: https://git.openjdk.org/jdk/pull/15417#discussion_r1304967438