On Mon, 5 Jan 2026 18:12:08 GMT, David Lloyd <[email protected]> wrote:
>> What you have done is fine. Thanks! However, there is one potential problem
>> left:
>> We are passing `tmpUid` to `getpwuid_r` as an `int`. That results in the
>> following sequence (example from AIX):
>>
>> [2.537s][trace][foreign,downcall] ;; { argument shuffle
>> [2.537s][trace][foreign,downcall] 0x0a0001000747d744: mr r12,r3
>> [2.537s][trace][foreign,downcall] 0x0a0001000747d748: extsw r3,r4
>> [2.537s][trace][foreign,downcall] 0x0a0001000747d74c: mr r4,r5
>> [2.537s][trace][foreign,downcall] 0x0a0001000747d750: mr r5,r6
>> [2.537s][trace][foreign,downcall] 0x0a0001000747d754: extsw r6,r7
>> [2.537s][trace][foreign,downcall] 0x0a0001000747d758: mr r7,r8
>> [2.537s][trace][foreign,downcall] ;; } argument shuffle
>>
>> The 4 Byte value for `tmpUid` is taken from Register r4, sign extended to 8
>> Byte long and put into the first argument register r3. The sign extend is
>> wrong because `uid` is an `uint32_t`. That violates the calling convention.
>> We have no way to tell the FFM that we need zero extend.
>>
>> A possible workaround would be to do the conversion in Java and passing it
>> as long:
>>
>> 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 ed520529ac8..573513b7bef 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
>> @@ -25,6 +25,7 @@
>>
>> package com.sun.security.auth.module;
>>
>> +import jdk.internal.util.Architecture;
>> import jdk.internal.util.OperatingSystem;
>>
>> import java.lang.foreign.AddressLayout;
>> @@ -83,6 +84,8 @@ public class UnixSystem {
>> = (ValueLayout.OfByte) LINKER.canonicalLayouts().get("char");
>> private static final ValueLayout.OfInt C_INT
>> = (ValueLayout.OfInt) LINKER.canonicalLayouts().get("int");
>> + private static final ValueLayout.OfLong C_LONG
>> + = (ValueLayout.OfLong) LINKER.canonicalLayouts().get("long");
>> private static final AddressLayout C_POINTER
>> = ((AddressLayout) LINKER.canonicalLayouts().get("void*"))
>>
>> .withTargetLayout(MemoryLayout.sequenceLayout(java.lang.Long.MAX_VALUE,
>> C_CHAR));
>> @@ -110,10 +113,14 @@ public class UnixSystem {
>>
>> // getpwuid_r does not work on AIX, instead we use another similar
>> function
>> // exter...
>
> FWIW there is an issue and ML discussion relating to extension of arguments
> with respect to `ValueLayout`: https://bugs.openjdk.org/browse/JDK-8336664
\What happens if you create a user on AIX with a uid bigger than 2^31 and call
`getpwuid_r` on it (by hardcoding `tmpUid` as a negative number)?
-------------
PR Review Comment: https://git.openjdk.org/jdk/pull/28931#discussion_r2662861217
