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SubjectRe: [PATCH] arm/arm64: smccc: Use xN for arm64 register constraints with clang
El Thu, Mar 22, 2018 at 04:19:42PM -0700 Greg Hackmann ha dit:

> On 03/22/2018 03:44 PM, Matthias Kaehlcke wrote:
> > El Thu, Mar 22, 2018 at 10:26:18PM +0000 Nick Desaulniers ha dit:
> >
> >> Note that a patch in this form has previously been implemented by:
> >>
> >> Andrey Konovalov <>:
> >>
> >>
> >> and another by:
> >>
> >> Greg Hackmann <>:
> >>
> >>
> >> If you used either as a reference, you may want to credit them with a
> >> `Suggested-by:` in the commit message.
> >
> > Not really, but I think I prefer Greg's version over mine and might
> > use it in a respin if nobody raises objections.
> NAK. There's a reason I didn't send my change upstream.
> As Marc pointed out (, the "r"
> prefix tells gcc to pick the appropriate register width. "x" makes it
> unconditionally use the entire 64-bit register width. Just swapping out
> one for the other changes the macro's semantics.
> Unfortunately since this was breaking builds in android-4.14 and we
> didn't have an immediate-term fix, I bit the bullet and added the above
> commit -- but *only* as a short-term workaround. For the one caller we
> currently have in 4.14.y, gcc was using the entire 64-bit width for all
> its inputs anyway, so "r" vs. "x" didn't make a difference. But that
> might not be true if/when someone introduces other SMCCC 1.1 callers.
> Unfortunately I don't see a better way to deal with this than waiting
> for clang to support "r"-style constraints on ARM64.

Thanks for the clarification! From the other thread
( I had the impression that ARM
folks saw the option of a mergeable fix.

Given the fact that clang support for kernel builds is still
recent/WIP I guess it's not the end of the world if we have to raise
the minimum clang version to 7.x for newer kernels.

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