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

[Mark Rutland]

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@xxxxxxx> 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.