RFR: 8277489: Rewrite JAAS UnixLoginModule with FFM [v8]

[Weijun Wang]

On Tue, 13 Jan 2026 21:17:13 GMT, Weijun Wang <weijun at openjdk.org> wrote:

>> Rewrite the native calls with FFM.
>
> Weijun Wang has updated the pull request incrementally with one additional commit since the last revision:
> 
>   new naming style; use VarHandle to access fields

A new commit pushed after some offline discussion. Now using a new naming style with an uppercase PREFIX followed by the original C name. For example, a `MethodHandle` for `getgroups` becomes `MH_getgroups`. Also, switching to `VarHandle` for struct field retrieval.

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PR Comment: https://git.openjdk.org/jdk/pull/28931#issuecomment-3746638101