RFR: 8277489: Rewrite JAAS UnixLoginModule with FFM [v2]

[Martin Doerr]

On Fri, 2 Jan 2026 15:35:49 GMT, Weijun Wang <weijun at openjdk.org> wrote:

>> src/jdk.security.auth/share/classes/com/sun/security/auth/module/UnixSystem.java line 96:
>> 
>>> 94:             .downcallHandle(SYMBOL_LOOKUP.findOrThrow("getpwuid_r"),
>>> 95:                     FunctionDescriptor.of(C_INT, C_INT, C_POINTER, C_POINTER,
>>> 96:                             C_LONG, C_POINTER));
>> 
>> `C_LONG` looks wrong for 32 bit platforms (arm 32). Note that `size_t` is supported by `canonicalLayouts`.
>
> Do you see 64 bit?
> <img width="588" height="306" alt="Screenshot 2026-01-02 at 10 26 20" src="https://github.com/user-attachments/assets/82106d61-27f8-4871-a890-039971665e62" />
> There is no arm32 here so I assume it will be the `FallbackLinker`. The size will be returned by a JNI function `ffi_sizeof_long()`. No idea how it could go wrong.

Right, arm32 is using the `FallbackLinker`. `size_t` is mapped here: https://github.com/openjdk/jdk/blob/2daf12edd24e641d4d7706d582994c2b3fe95e87/src/java.base/share/classes/jdk/internal/foreign/abi/fallback/FallbackLinker.java#L311
which takes it from here:
https://github.com/openjdk/jdk/blob/2daf12edd24e641d4d7706d582994c2b3fe95e87/src/java.base/share/classes/jdk/internal/foreign/abi/fallback/FFIType.java#L59
@bulasevich: You may want to try on arm32.

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PR Review Comment: https://git.openjdk.org/jdk/pull/28931#discussion_r2657948890