Re: [PATCH 14/14] selftests/timers/auxclock: Test vDSO functionality

["Thomas Weißschuh" <thomas.weissschuh@linutronix.de>]

On Sun, Jul 06, 2025 at 10:26:31PM +0200, Thomas Gleixner wrote:
> On Tue, Jul 01 2025 at 10:58, Thomas Weißschuh wrote:
> 
> > Extend the auxclock test to also cover the vDSO.
> 
> I'm not really convinved, that this is the right thing to do. Why can't
> this just extend selftests/vDSO instead of creating these
> 
> > +#include "../vDSO/parse_vdso.c"
> > +#include "../vDSO/vdso_config.h"
> > +#include "../vDSO/vdso_call.h"
> 
> cross directory oddities? Confused.

Then we'd have to duplicate the auxclock management into the vDSO selftests.
And the knowledge about the expected clock_getres() return values.

In general I think we need to introduce some reuse of the vDSO parsing code
from other selftests in any case. For example the timens selftests call the
vDSO by just invoking the libc wrappers. But the libc may not support a vDSO,
have it disabled for some reason or the vDSO itself falls back to a syscall.
I intend to introduce some vDSO accessors which force the usage of the vDSO
fastpath by using parse_vdso.c to directly call into the vDSO and seccomp to
inhibit the fallback syscalls.

Or, to avoid a dependency we could move the vDSO parsing one step up to
tools/testing/selftests/vdso_support.h, and clean up the interfaces.


Thomas