On Fri, 13 Oct 2023 13:37:10 GMT, Jorn Vernee <jver...@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 of the existing 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. > > 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. > Okay, so it sounds like Java double on AIX is still 8-byte aligned, but the > native double is 4-byte aligned? Correct within structures. I believe they are always 8-byte aligned except in structures which are packed more densely. > In that case, I'd say that passing `JAVA_DOUBLE` as an argument resulting in > an exception, is expected behavior. Hmm... Should we disallow to pass 8-byte aligned double values? Fixing the tests is a good thing. But, I have a different concern: I guess many developers may use them without testing on AIX. This would cause problems which we could avoid by supporting 8-byte aligned doubles in addition. What about adding layouts.put("jdouble", ValueLayout.JAVA_DOUBLE.withByteAlignment(4)); layouts.put("aligneddouble", ValueLayout.JAVA_DOUBLE); // allowed for usage outside of structures ? ------------- PR Review Comment: https://git.openjdk.org/jdk/pull/16179#discussion_r1358281371
