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

Masahiro Yamada
2019-10-24T14:39:18Z

On Thu, Oct 24, 2019 at 10:28 PM Mark Rutland <mark.rutland@arm.com> wrote:
>
> On Tue, Oct 22, 2019 at 12:26:02PM -0700, Sami Tolvanen wrote:
> > On Tue, Oct 22, 2019 at 9:28 AM Mark Rutland <mark.rutland@arm.com> wrote:
>
> > > > +config SHADOW_CALL_STACK
> > > > + bool "Clang Shadow Call Stack"
> > > > + depends on ARCH_SUPPORTS_SHADOW_CALL_STACK
> > > > + depends on CC_IS_CLANG && CLANG_VERSION >= 70000
> > >
> > > Is there a reason for an explicit version check rather than a
> > > CC_HAS_<feature> check? e.g. was this available but broken in prior
> > > versions of clang?
> >
> > No, this feature was added in Clang 7. However,
> > -fsanitize=shadow-call-stack might require architecture-specific
> > flags, so a simple $(cc-option, -fsanitize=shadow-call-stack) in
> > arch/Kconfig is not going to work. I could add something like this to
> > arch/arm64/Kconfig though:
> >
> > select ARCH_SUPPORTS_SHADOW_CALL_STACK if CC_HAVE_SHADOW_CALL_STACK
> > ...
> > config CC_HAVE_SHADOW_CALL_STACK
> > def_bool $(cc-option, -fsanitize=shadow-call-stack -ffixed-x18)
> >
> > And then drop CC_IS_CLANG and version check entirely. Thoughts?
>
> That sounds good to me, yes!
>
> Thanks,
> Mark.

If you use cc-option, please add a comment like

# supported by Clang 7 or later.

I do not know the minimal supported clang version.
When we bump the minimal version to clang 7,
we can drop the cc-option test entirely.

--
Best Regards
Masahiro Yamada