@rustbot label +stable-nominated

On AIX, <sys/stat.h> declares field tv_nsec of struct timespec as long, but the underlying system calls return a 4-byte value in both 32-bit and 64-bit modes. This PR changes to declare tv_nsec as i32 in the libc crate to avoid including the other undefined 4 bytes in the 64-bit mode.

I think this is reasonable to change on our side, but isn't it a problem for C users as well if the header doesn't match the syscalls? Technically posix specifies tv_nsec as long too https://pubs.opengroup.org/onlinepubs/009695399/basedefs/time.h.html so I'm surprised the syscalls differ (X32 is a weird exception here)

On AIX, <sys/stat.h> declares field tv_nsec of struct timespec as long, but the underlying system calls return a 4-byte value in both 32-bit and 64-bit modes. This PR changes to declare tv_nsec as i32 in the libc crate to avoid including the other undefined 4 bytes in the 64-bit mode.

I think this is reasonable to change on our side, but isn't it a problem for C users as well if the header doesn't match the syscalls? Technically posix specifies tv_nsec as long too https://pubs.opengroup.org/onlinepubs/009695399/basedefs/time.h.html so I'm surprised the syscalls differ (X32 is a weird exception here)

The problem can be reproduced with a C test case as well. AIX should have mapped stat and its variants to a new set of ABIs that return tv_nsec as a long when compiling for POSIX code, but it appears that this was not done. However, AIX provides something such as the statx system call that accepts two additional arguments, including Command. The caller can specify the STX_TIMESPEC flag to use struct timespec instead of st_timespec. In 64-bit mode, this flag causes statx to treat tv_nsec as an 8-byte value. However, the actual value returned in tv_nsec is still only 4 bytes, with the upper 4 bytes cleared, no additional precision is provided.

Exposing statx and the other stat variants with the x suffix, along with the full set of flags for the Command flag definitions, and implementing Rust’s stat functions on top of them would be quite complex. Moreover, doing so would not provide any real benefit, since no extra precision is gained. On the other hand, the libc crate already contains code to handle a similar situation on x86, where tv_nsec is always 8 bytes in both 32-bit and 64-bit modes. After discussion internally, we thought it would be cleaner to do the same for AIX.

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.