[PATCH] arm64: Work around broken GCC handling of "S" constraint

[Ard Biesheuvel]

On Mon, 7 Dec 2020 at 18:41, Marc Zyngier <maz at kernel.org> wrote:
>
> On 2020-12-07 17:19, Ard Biesheuvel wrote:
> > (resend with David's email address fixed)
>
> Irk. Thanks for that.
>
> >> > +#ifdef CONFIG_CC_HAS_BROKEN_S_CONSTRAINT
> >> > +#define SYM_CONSTRAINT "i"
> >> > +#else
> >> > +#define SYM_CONSTRAINT "S"
> >> > +#endif
> >> > +
> >>
> >> Could we just check GCC_VERSION here?
>
> I guess we could. But I haven't investigated which exact range of
> compiler is broken (GCC 6.3 seems fixed, but that's the oldest
> I have apart from the offending 4.9).
>

I tried 5.4 on godbolt, and it seems happy. And the failure will be
obvious, so we can afford to get it slightly wrong and refine it
later.