Re: [PATCH 06/18] add support for Clang's Shadow Call Stack (SCS)

[Nick Desaulniers]

On Fri, Oct 18, 2019 at 11:33 AM Miguel Ojeda
<miguel.ojeda.sandonis@xxxxxxxxx> wrote:
>
> On Fri, Oct 18, 2019 at 7:11 PM Sami Tolvanen <samitolvanen@xxxxxxxxxx> wrote:
> >
> > On Fri, Oct 18, 2019 at 10:08 AM 'Nick Desaulniers' via Clang Built
> > Linux <clang-built-linux@xxxxxxxxxxxxxxxx> wrote:
> > > > diff --git a/include/linux/compiler-clang.h b/include/linux/compiler-clang.h
> > > > index 333a6695a918..9af08391f205 100644
> > > > --- a/include/linux/compiler-clang.h
> > > > +++ b/include/linux/compiler-clang.h
> > > > @@ -42,3 +42,5 @@
> > > >   * compilers, like ICC.
> > > >   */
> > > >  #define barrier() __asm__ __volatile__("" : : : "memory")
> > > > +
> > > > +#define __noscs                __attribute__((no_sanitize("shadow-call-stack")))
> > >
> > > It looks like this attribute, (and thus a requirement to use this
> > > feature), didn't exist until Clang 7.0: https://godbolt.org/z/p9u1we
> > > (as noted above)
> > >
> > > I think it's better to put __noscs behind a __has_attribute guard in
> > > include/linux/compiler_attributes.h.  Otherwise, what will happen when
> > > Clang 6.0 sees __noscs, for example? (-Wunknown-sanitizers will
> > > happen).
> >
> > Good point, I'll fix this in v2. Thanks.
>
> +1, please CC whenever you send it!

Sami pointed out to me off thread that __has_attribute would only
check `no_sanitize`, not `shadow-call-stack`.  So maybe best to keep
the definition here (include/linux/compiler-clang.h), but wrapped in a
`__has_feature` check so that Clang 6.0 doesn't start complaining.
-- 
Thanks,
~Nick Desaulniers