Re: [PATCH -tip 1/2] Kconfig: Bump required compiler version of KASAN and UBSAN

[Marco Elver]

On Tue, 2 Jun 2020 at 21:19, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
>
> On Tue, Jun 02, 2020 at 11:57:15AM -0700, Nick Desaulniers wrote:
> > On Tue, Jun 2, 2020 at 11:44 AM 'Marco Elver' via Clang Built Linux
> > <clang-built-linux@xxxxxxxxxxxxxxxx> wrote:
> > >
> > > Adds config variable CC_HAS_WORKING_NOSANITIZE, which will be true if we
> > > have a compiler that does not fail builds due to no_sanitize functions.
> > > This does not yet mean they work as intended, but for automated
> > > build-tests, this is the minimum requirement.
> > >
> > > For example, we require that __always_inline functions used from
> > > no_sanitize functions do not generate instrumentation. On GCC <= 7 this
> > > fails to build entirely, therefore we make the minimum version GCC 8.
> > >
> > > For KCSAN this is a non-functional change, however, we should add it in
> > > case this variable changes in future.
> > >
> > > Link: https://lkml.kernel.org/r/20200602175859.GC2604@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
> > > Suggested-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> > > Signed-off-by: Marco Elver <elver@xxxxxxxxxx>
> >
> > Is this a problem only for x86?  If so, that's quite a jump in minimal
> > compiler versions for a feature that I don't think is currently
> > problematic for other architectures?  (Based on
> > https://lore.kernel.org/lkml/20200529171104.GD706518@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/
> > )
>
> Currently x86 only, but I know other arch maintainers are planning to
> have a hard look at their code based on our findings.

I've already spotted a bunch of 'noinstr' outside arch/x86 e.g. in
kernel/{locking,rcu}, and a bunch of these functions use atomic_*, all
of which are __always_inline. The noinstr uses outside arch/x86 would
break builds on all architecture with GCC <= 7 when using sanitizers.
At least that's what led me to conclude we need this for all
architectures.

Thanks,
-- Marco