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Re: [XEN PATCH][for-4.19 v4 1/8] xen/include: add macro ISOLATE_LOW_BIT
- To: Nicola Vetrini <nicola.vetrini@xxxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Thu, 9 Nov 2023 08:18:34 +0100
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- Cc: michal.orzel@xxxxxxx, xenia.ragiadakou@xxxxxxx, ayan.kumar.halder@xxxxxxx, consulting@xxxxxxxxxxx, andrew.cooper3@xxxxxxxxxx, roger.pau@xxxxxxxxxx, Simone Ballarin <simone.ballarin@xxxxxxxxxxx>, Doug Goldstein <cardoe@xxxxxxxxxx>, George Dunlap <george.dunlap@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Wei Liu <wl@xxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Thu, 09 Nov 2023 07:19:05 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
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.
Jan
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