On Wed, Mar 25, 2020 at 12:54:10PM +0100, Ard Biesheuvel wrote:
> On Wed, 25 Mar 2020 at 12:50, Mark Brown <broonie@kernel.org> wrote:

> > Since BTI is a mandatory feature of v8.5 there is no BTI arch_extension,
> > you can only enable it by moving the base architecture to v8.5.  You'd
> > need to use .arch and that feels likely to find us sharp edges to run
> > into.

> I think we should talk to the toolchain folks about this. Even if
> .arch_extension today does not support the 'bti' argument, it *is*
> most definitely an architecture extension, even it it is mandatory in
> v8.5 (given that v8.5 is itself an architecture extension).

I agree entirely, the current behaviour is surprising and doesn't really
map onto how the architecture is described - my first thought was
similar to yours.  It won't help us right now but it would help for
future architecture extensions and for other projects.