Re: [PATCH v8 00/12] add support for Clang's Shadow Call Stack

From: Sami Tolvanen
Date: Wed Feb 19 2020 - 15:12:36 EST

On Wed, Feb 19, 2020 at 10:38 AM James Morse <james.morse@xxxxxxx> wrote:
> This looks like reserving x18 is causing Clang to not-inline the __kern_hyp_va() calls,
> losing the vitally important section information. (I can see why the compiler thinks this
> is fair)

Thanks for catching this. This doesn't appear to be caused by
reserving x18, it looks like SCS itself is causing clang to avoid
inlining these. If I add __noscs to __kern_hyp_va(), clang inlines the
function again. __always_inline also works, as you pointed out.

> Is this a known, er, thing, with clang-9?

I can reproduce this with ToT clang as well.

> I suspect repainting all KVM's 'inline' with __always_inline will fix it. (yuck!) I'll try
> tomorrow.

I think switching to __always_inline is the correct solution here.