[PATCH v2 2/7] y2038: Introduce __ASSUME_64BIT_TIME define

[Joseph Myers]

On Wed, 8 May 2019, Lukasz Majewski wrote:

> The 64 bit versions of syscalls (like clock_settime64 or
> clock_gettime64) are available since 5.1 kernel (as you posted already
> the following patch: "Update syscall-names.list for Linux 5.1" .
> 
> I've now only focused on clock_settime(64) to make the discussion more
> concrete.

The following will be relevant for use of clock_gettime64, but is not 
immediately relevant for clock_settime64:

clock_gettime64 will complicate things because the present clock_gettime 
code uses the vDSO on some architectures.  Is clock_gettime64 available in 
the vDSO in 5.1 on all architectures where clock_gettime is?  If it is, 
with the same symbol version as used for existing vDSO symbols, or a 
different symbol version?  If not in the vDSO, are there any performance 
implications from using a clock_gettime64 syscall in place of a 
clock_gettime call to the vDSO?

(I think the code using the vDSO will automatically fall back to a 
corresponding syscall if the vDSO symbol isn't there, but answers to those 
questions will still be relevant for reviewing any patch for 
clock_gettime64 and understanding exactly what code paths it will use.)

-- 
Joseph S. Myers
joseph@codesourcery.com