Messages in this thread |  | | From | Nick Desaulniers <> | Date | Thu, 05 Apr 2018 18:43:05 +0000 | Subject | Re: [PATCH] arm/arm64: smccc: Use xN for arm64 register constraints with clang |
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On Thu, Mar 22, 2018 at 4:58 PM Matthias Kaehlcke <mka@chromium.org> wrote:
> El Thu, Mar 22, 2018 at 04:19:42PM -0700 Greg Hackmann ha dit: > > 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.
Manoj fixed this in: https://reviews.llvm.org/rL328829 https://bugs.llvm.org/show_bug.cgi?id=36862
Looks set to ride the Clang 6.0 train. mka@ if you're planning another state of the union email, it would be good to note the clang 6.0 requirement for arm64.
Is there anything left to do here? -- Thanks, ~Nick Desaulniers
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