Messages in this thread |  | | Date | Thu, 22 Mar 2018 16:58:11 -0700 | From | Matthias Kaehlcke <> | Subject | Re: [PATCH] arm/arm64: smccc: Use xN for arm64 register constraints with clang |
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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 <andreyknvl@google.com>: > >> https://gist.github.com/xairy/ee11682ea86044a45c0291c528cd936f > >> > >> and another by: > >> > >> Greg Hackmann <ghackmann@google.com>: > >> https://android-review.googlesource.com/c/kernel/common/+/645181 > >> > >> 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 (https://lkml.org/lkml/2018/3/16/987), 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 (https://lkml.org/lkml/2018/3/1/268) 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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