RFR: 8277489: Rewrite JAAS UnixLoginModule with FFM [v5]

[Martin Doerr]

On Mon, 5 Jan 2026 16:06:56 GMT, Weijun Wang <weijun at openjdk.org> wrote:

> Maybe we can call Integer.toUnsignedLong() on pw_uid and pw_gid? In UnixSystem, they are longs.

Yes, I had thought about this, too. But, I think we will need to distinguish between the platforms. PPC64 and s390 (and also SPARC which is no longer supported) pass smaller integer type values as 64 bit `long` and `Integer.toUnsignedLong()` would be correct when we change the signature to use `long` instead of `int`.
However, other platforms may require to pass the values as 4 Byte `int`. Especially when they are passed on stack. (Not sure if any supported platform does that. Probably not.) It's unfortunate that the FFM doesn't provide a good abstraction for passing `uint32_t`. Maybe we should implement an enhancement?
In hotspot, `CCallingConventionRequiresIntsAsLongs` is used to decide if 4 Byte integer types need to get extended.

> I would suggest we just throw an exception in UnixSystem if getpwuid_r cannot find the username.

Fine with me. I don't like ignoring getpwuid_r failures, either.

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PR Review Comment: https://git.openjdk.org/jdk/pull/28931#discussion_r2662113718