Re: [XEN PATCH][for-4.19 v4 1/8] xen/include: add macro ISOLATE_LOW_BIT

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Thu, 9 Nov 2023, Jan Beulich wrote:
> On 31.10.2023 08:43, Jan Beulich wrote:
> > What I would consider scope creep I
> > specifically didn't even ask for: I'd like this macro to be overridable
> > by an arch. Specifically (see my earlier naming hint) I'd like to use
> > x86's BMI insn BLSI in the context of "x86: allow Kconfig control over
> > psABI level", when ABI v2 or higher is in use.
> 
> Actually I need to withdraw that. It meanwhile occurred to me that the
> compiler ought to recognize this pattern. And indeed gcc doesn't even
> have a builtin for it; its BMI intrinsic for BLSI (on x86 that is)
> specifically expands to x & -x, which the backend then is expected to
> deal with as appropriate. And indeed it can be observed to, with my
> "x86: allow Kconfig control over psABI level" in place.
> 
> Just as a reminder: I'd still like to see the further renaming done
> (to ISOLATE_LSB()). If I was to commit this patch, I'd be fine doing
> so while committing.

Please do