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Date:   Thu, 24 Oct 2019 14:28:32 +0100
From:   Mark Rutland <mark.rutland@arm.com>
To:     Sami Tolvanen <samitolvanen@google.com>
Cc:     Will Deacon <will@kernel.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Steven Rostedt <rostedt@goodmis.org>,
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Subject: Re: [PATCH 06/18] add support for Clang's Shadow Call Stack (SCS)
Message-ID: <20191024132832.GG4300@lakrids.cambridge.arm.com>
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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.