linux-kernel - Re: [kvm-unit-tests PATCH 0/3] Fix arm64 clang errors on fpu tests

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Message-ID: <20241023-f6a2a8d9fdea565838175648@orel>
Date: Wed, 23 Oct 2024 10:03:26 +0200
From: Andrew Jones <andrew.jones@...ux.dev>
To: Raghavendra Rao Ananta <rananta@...gle.com>
Cc: Subhasish Ghosh <subhasish.ghosh@....com>, 
	Joey Gouly <joey.gouly@....com>, Oliver Upton <oliver.upton@...ux.dev>, 
	Marc Zyngier <maz@...nel.org>, linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev, 
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [kvm-unit-tests PATCH 0/3] Fix arm64 clang errors on fpu tests

On Tue, Oct 22, 2024 at 01:31:24PM -0700, Raghavendra Rao Ananta wrote:
> Hi Andrew,
> 
> >
> > With clang 18.1.8 (Fedora 18.1.8-1.fc40) I get a bunch of errors like
> > these
> >
> >     arm/fpu.c:281:3: error: instruction requires: fp-armv8
> >
> > I used my cross-clang series[1] and configured with
> >
> >     ./configure --arch=arm64 --cc=clang --cflags='--target=aarch64'
> --cross-prefix=aarch64-linux-gnu-
> >
> > [1]
> https://lore.kernel.org/all/20240911091406.134240-7-andrew.jones@linux.dev/
> >
> > Thanks,
> > drew
> 
> I was able to reproduce the errors by pointing to a newer clang (20) and
> applying your series.
> I think we see the errors because llvm decided to disable loads and stores
> on FP registers with "-mgeneral-regs-only" [1]. Explicitly adding
> ".arch_extension fp" for the fp_reg_{read,write}() helped with the build:
> 
> diff --git a/arm/fpu.c b/arm/fpu.c
> index 6b0411d3..f44ed82a 100644
> --- a/arm/fpu.c
> +++ b/arm/fpu.c
> @@ -38,7 +38,8 @@ static inline bool arch_collect_entropy(uint64_t *random)
>  #define fpu_reg_read(val)                              \
>  ({                                                     \
>         uint64_t *__val = (val);                        \
> -       asm volatile("stp q0, q1, [%0], #32\n\t"        \
> +       asm volatile(".arch_extension fp\n"             \
> +                    "stp q0, q1, [%0], #32\n\t"        \
>                      "stp q2, q3, [%0], #32\n\t"        \
>                      "stp q4, q5, [%0], #32\n\t"        \
>                      "stp q6, q7, [%0], #32\n\t"        \
> @@ -71,7 +72,8 @@ static inline bool arch_collect_entropy(uint64_t *random)
>  #define fpu_reg_write(val)                             \
>  do {                                                   \
>         uint64_t *__val = (val);                        \
> -       asm volatile("ldp q0, q1, [%0], #32\n\t"        \
> +       asm volatile(".arch_extension fp\n"             \
> +                    "ldp q0, q1, [%0], #32\n\t"        \
>                      "ldp q2, q3, [%0], #32\n\t"        \
>                      "ldp q4, q5, [%0], #32\n\t"        \
>                      "ldp q6, q7, [%0], #32\n\t"        \
> 
> If you are fine with this, I can push it as a separate patch in v2.

The fix works for me too. Please post v2.

Thanks,
drew