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

[Weijun Wang]

On Mon, 5 Jan 2026 11:42:08 GMT, Martin Doerr <mdoerr at openjdk.org> wrote:

>> Or I can call this `_posix_getpwuid_r` function if `isAix()` is true. Is this enough?
>> 
>>      private static final MethodHandle getpwuid_r = LINKER
>> -            .downcallHandle(SYMBOL_LOOKUP.findOrThrow("getpwuid_r"),
>> +            .downcallHandle(SYMBOL_LOOKUP.findOrThrow(
>> +                            OperatingSystem.isAix() ? "_posix_getpwuid_r" : "getpwuid_r"),
>>                      FunctionDescriptor.of(C_INT, C_INT, C_POINTER, C_POINTER,
>> -                            C_SIZE_T, C_POINTER));
>> +                            OperatingSystem.isAix() ? C_INT : C_SIZE_T,
>> +                            C_POINTER));
>
> Thank you for taking care of it! I appreciate it. This has worked:
> 
> diff --git a/src/jdk.security.auth/share/classes/com/sun/security/auth/module/UnixSystem.java b/src/jdk.security.auth/share/classes/com/sun/security/auth/module/UnixSystem.java
> index ee2c5effcf0..3afab6f7974 100644
> --- a/src/jdk.security.auth/share/classes/com/sun/security/auth/module/UnixSystem.java
> +++ b/src/jdk.security.auth/share/classes/com/sun/security/auth/module/UnixSystem.java
> @@ -38,6 +38,8 @@
>  import java.lang.invoke.MethodHandle;
>  import java.lang.invoke.VarHandle;
>  
> +import jdk.internal.util.OperatingSystem;
> +
>  import static java.lang.foreign.MemoryLayout.PathElement.groupElement;
>  
>  /**
> @@ -106,9 +108,9 @@ public class UnixSystem {
>              .downcallHandle(SYMBOL_LOOKUP.findOrThrow("getgid"),
>                      FunctionDescriptor.of(C_INT));
>      private static final MethodHandle getpwuid_r = LINKER
> -            .downcallHandle(SYMBOL_LOOKUP.findOrThrow("getpwuid_r"),
> +            .downcallHandle(SYMBOL_LOOKUP.findOrThrow(OperatingSystem.isAix() ? "_posix_getpwuid_r" : "getpwuid_r"),
>                      FunctionDescriptor.of(C_INT, C_INT, C_POINTER, C_POINTER,
> -                            C_SIZE_T, C_POINTER));
> +                            OperatingSystem.isAix() ? C_INT : C_SIZE_T, C_POINTER));
>  
>      private static final GroupLayout passwd_layout = MemoryLayout.structLayout(
>              C_POINTER.withName("pw_name"),
> @@ -136,7 +138,7 @@ public class UnixSystem {
>      // sysconf(_SC_GETPW_R_SIZE_MAX) on macOS is 4096 and 1024 on Linux.
>      // Not calling sysconf() here because _SC_GETPW_R_SIZE_MAX is different
>      // on different platforms.
> -    private static final long GETPW_R_SIZE_MAX = 4096L;
> +    private static final int GETPW_R_SIZE_MAX = 4096;
>  
>      /**
>       * Instantiate a {@code UnixSystem} and load
> 
> Note that `GETPW_R_SIZE_MAX` needs to be an `int` because `long` to `int` conversion would require an explicit cast (probably also for arm32). The other way round works implicitly.
> 
> I'd like to have feedback from the AIX experts as well. They may still be on vacation for a couple of days.
> 
> We still have a potential problem with the UID parameter. We are using an `int`, but the C code expects an `uint32_t`. Some platforms pass 32 bit values in 64 bit registers and expect a proper extension (zero for unsigned and sign for signed). If the UID becomes larger than INT_MAX, we use sign extend which is wrong.
> Not sure of anyone uses so large UIDs and if we could re...

Maybe we can call `Integer.toUnsignedLong()` on `pw_uid` and `pw_gid`? In `UnixSystem`, they are `long`s.

Also, I want to discuss on the `username` issue again. Do you think it's good to login successfully without a `UnixPrincipal`? Now that there is a way on AIX to get it, I'm more inclined to revert the changes made to `UnixLoginModule`. While the old `Unix.c` seems to support username being `null` we know it would fail later with an NPE so this has never really worked before. My current understanding is that silent passing the login without a username might hide a bug and if the user takes it for granted that there should be a `UnixPrincipal` there will be a problem sooner or later. In fact, I would suggest we just throw an exception in `UnixSystem` if `getpwuid_r` cannot find the username.

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PR Review Comment: https://git.openjdk.org/jdk/pull/28931#discussion_r2662017228