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

[Jorn Vernee]

On Fri, 13 Oct 2023 12:34:53 GMT, Martin Doerr <mdoerr at openjdk.org> wrote:

> I guess changing it would probably be better?

Yeah, I think so.

> Note that we will need something which maps to the 8-Byte aligned double. Otherwise we get an Exception when passing a JAVA_DOUBLE as normal argument.

Okay, so it sounds like Java double on AIX is still 8-byte aligned, but the native double is 4-byte aligned?

In that case, I'd say that passing `JAVA_DOUBLE` as an argument resulting in an exception, is expected behavior. Using `JAVA_DOUBLE` to link native functions works more or less by coincidence, since it has the same layout as the native `double`, on all other platforms. The AIX issue with double is not dissimilar to using JAVA_LONG to link against a function taking a native `long` on Windows, in which case the size of the type doesn't match.

The philosophy here is: a client is responsible for passing the right FunctionDescriptor/layouts, that matches the native function declaration. On AIX, JAVA_DOUBLE is just never the right layout, and the linker detects this and throws an exception.

I understand that some tests might be lazy and use JAVA_DOUBLE to link functions. It is fine to update those tests, e.g. to use C_DOUBLE defined in NativeTestHelper.

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PR Review Comment: https://git.openjdk.org/jdk/pull/16179#discussion_r1358238373