linux-kernel - Re: [PATCH 1/3] arm: include: asm: swab: mask rev16 instruction for clang

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Date:   Tue, 27 Jul 2021 10:53:20 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Pavo Banicevic <pavo.banicevic@...tura.hr>,
        Arnd Bergmann <arnd@...aro.org>
Cc:     linux@...linux.org.uk, ast@...nel.org, daniel@...earbox.net,
        andrii@...nel.org, kafai@...com, songliubraving@...com, yhs@...com,
        john.fastabend@...il.com, kpsingh@...nel.org, nathan@...nel.org,
        ivan.khoronzhuk@...aro.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        bpf@...r.kernel.org, clang-built-linux@...glegroups.com,
        matt.redfearn@...s.com, mingo@...nel.org, dvlasenk@...hat.com,
        juraj.vijtiuk@...tura.hr, robert.marko@...tura.hr,
        luka.perkov@...tura.hr, jakov.petrina@...tura.hr
Subject: Re: [PATCH 1/3] arm: include: asm: swab: mask rev16 instruction for clang

On Tue, Jul 27, 2021 at 7:12 AM Pavo Banicevic
<pavo.banicevic@...tura.hr> wrote:
>
> From: Ivan Khoronzhuk <ivan.khoronzhuk@...aro.org>
>
> The samples/bpf with clang -emit-llvm reuses linux headers to build
> bpf samples, and this w/a only for samples (samples/bpf/Makefile
> CLANG-bpf).
>
> It allows to build samples/bpf for arm bpf using clang.
> In another way clang -emit-llvm generates errors like:
>
> CLANG-bpf  samples/bpf/tc_l2_redirect_kern.o
> <inline asm>:1:2: error: invalid register/token name
> rev16 r3, r0
>
> This decision is arguable, probably there is another way, but
> it doesn't have impact on samples/bpf, so it's easier just ignore
> it for clang, at least for now.

NACK

The way to fix these is to sort out the header includes, not turning
off arbitrary things that are used by the actual kernel build for 32b
ARM.

>
> Signed-off-by: Ivan Khoronzhuk <ivan.khoronzhuk@...aro.org>
> ---
>  arch/arm/include/asm/swab.h | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/arch/arm/include/asm/swab.h b/arch/arm/include/asm/swab.h
> index c6051823048b..a9fd9cd33d5e 100644
> --- a/arch/arm/include/asm/swab.h
> +++ b/arch/arm/include/asm/swab.h
> @@ -25,8 +25,11 @@ static inline __attribute_const__ __u32 __arch_swahb32(__u32 x)
>         __asm__ ("rev16 %0, %1" : "=r" (x) : "r" (x));
>         return x;
>  }
> +
> +#ifndef __clang__
>  #define __arch_swahb32 __arch_swahb32
>  #define __arch_swab16(x) ((__u16)__arch_swahb32(x))
> +#endif
>
>  static inline __attribute_const__ __u32 __arch_swab32(__u32 x)
>  {
> --
> 2.32.0
>


-- 
Thanks,
~Nick Desaulniers