Re: [PATCH 1/7] x86/vdso: Respect COMPAT_32BIT_TIME

[Thomas Weißschuh]

On Tue, Mar 03, 2026 at 09:50:33PM +0100, Arnd Bergmann wrote:
> On Tue, Mar 3, 2026, at 19:11, H. Peter Anvin wrote:
> > On 2026-02-27 01:34, Thomas Weißschuh wrote:
> >>>>
> >>> The thing about gettimeofday() and time() is that they don't have
> >>> a 64-bit version and libc implementations are expected to call
> >>> clock_gettime() instead. The result was that there was never a
> >>> patch to turn the off either.
> >> 
> >> gettimeofday() is currently the only way to get the timezone of the kernel.
> >> But I guess this is a legacy thing anyways. If you say we should drop it,
> >> let's drop it.
> >> 
> >
> > The time zone in the kernel has never worked anyway, as it would require the
> > kernel to contain at least the forward portion of the zoneinfo/tzdata table in
> > order to actually work correctly. The only plausible use of it would be for
> > local time-based filesystems like FAT, but I don't think we bother.
> >
> > A bigger question is whether or not we should omit these from the vDSO
> > completely (potentially causing link failures) or replace them with stubs
> > returning -ENOSYS.
> 
> I see no harm in keeping gettimeofday() in the vdso when
> COMPAT_32BIT_TIME is turned on, as existing code will call it
> no matter whether it's in the vdso or the syscall.

We would still always keep them for 64-bit ABIs, right?

> Equally, I see no point in having either version of
> gettimeofday() or settimeofday() when COMPAT_32BIT_TIME is
> disabled, as clearly anything calling it would pass incorrect
> data for times past 2038.

Should we also drop the syscalls in these cases?
We will need to keep settimeofday() in some form to support the
timewarping call done by init.

Recap/Proposal:

* Keep the gettimeofday()/time() syscalls when they are y2038 safe or
  CONFIG_COMPAT_32BIT_TIME is set.
* Always provide settimeofday(). If CONFIG_COMPAT_32BIT_TIME is *not*
  set, reject passing any 'tv' argument where it may not be y2038 safe.
* The vDSO functions always mirror the systemcall availability.


Thomas