Re: [PATCH v6 01/19] kernel: Standardize vdso_datapage

[Huw Davies]

On Tue, Jun 04, 2019 at 01:05:40PM +0100, Vincenzo Frascino wrote:
> On 31/05/2019 09:16, Arnd Bergmann wrote:
> > On Thu, May 30, 2019 at 4:15 PM Vincenzo Frascino
> > <vincenzo.frascino@xxxxxxx> wrote:
> > 
> >> + * vdso_data will be accessed by 64 bit and compat code at the same time
> >> + * so we should be careful before modifying this structure.
> >> + */
> >> +struct vdso_data {
> >> +       u32                     seq;
> >> +
> >> +       s32                     clock_mode;
> >> +       u64                     cycle_last;
> >> +       u64                     mask;
> >> +       u32                     mult;
> >> +       u32                     shift;
> >> +
> >> +       struct vdso_timestamp   basetime[VDSO_BASES];
> >> +
> >> +       s32                     tz_minuteswest;
> >> +       s32                     tz_dsttime;
> >> +       u32                     hrtimer_res;
> >> +};
> > 
> > The structure contains four padding bytes at the end, which is
> > something we try to avoid, at least if this ends up being used as
> > an ABI. Maybe add "u32 __unused" at the end?
> > 
> 
> Agreed, I will fix this in v7.

Note that this is also necessary to ensure that CLOCK_MONOTONIC_RAW
works in the 32-bit vDSO on x86_64 kernels.

Huw.