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From: Yonghong Song <yhs@fb.com>
To: Pavo Banicevic <pavo.banicevic@sartura.hr>,
	<linux@armlinux.org.uk>, <ast@kernel.org>, <daniel@iogearbox.net>,
	<andrii@kernel.org>, <kafai@fb.com>, <songliubraving@fb.com>,
	<john.fastabend@gmail.com>, <kpsingh@kernel.org>,
	<nathan@kernel.org>, <ndesaulniers@google.com>,
	<ivan.khoronzhuk@linaro.org>,
	<linux-arm-kernel@lists.infradead.org>,
	<linux-kernel@vger.kernel.org>, <netdev@vger.kernel.org>,
	<bpf@vger.kernel.org>, <clang-built-linux@googlegroups.com>,
	<matt.redfearn@mips.com>, <mingo@kernel.org>,
	<dvlasenk@redhat.com>, <juraj.vijtiuk@sartura.hr>,
	<robert.marko@sartura.hr>, <luka.perkov@sartura.hr>,
	<jakov.petrina@sartura.hr>
Subject: Re: [PATCH 1/3] arm: include: asm: swab: mask rev16 instruction for clang
Date: Tue, 27 Jul 2021 08:46:23 -0700	[thread overview]
Message-ID: <424add3f-d79a-79dd-2e6a-dbb966bf7349@fb.com> (raw)
In-Reply-To: <20210727141119.19812-2-pavo.banicevic@sartura.hr>



On 7/27/21 7:11 AM, Pavo Banicevic wrote:
> From: Ivan Khoronzhuk <ivan.khoronzhuk@linaro.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.
> 
> Signed-off-by: Ivan Khoronzhuk <ivan.khoronzhuk@linaro.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

What if the kernel is compiled with clang compiler?
Does this still work?

To workaround samples/bpf issue, I think you can use
__BPF_TRACING__ macro.

>   
>   static inline __attribute_const__ __u32 __arch_swab32(__u32 x)
>   {
> 

  reply	other threads:[~2021-07-27 15:47 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-27 14:11 [PATCH 0/3] Address compilation of eBPF related software with clang compiler on arm architecture Pavo Banicevic
2021-07-27 14:11 ` [PATCH 1/3] arm: include: asm: swab: mask rev16 instruction for clang Pavo Banicevic
2021-07-27 15:46   ` Yonghong Song [this message]
2021-07-27 17:53   ` Nick Desaulniers
2021-07-27 21:43     ` Andrii Nakryiko
2021-07-27 14:11 ` [PATCH 2/3] arm: include: asm: unified: mask .syntax unified " Pavo Banicevic
2021-07-27 17:55   ` Nick Desaulniers
2021-07-27 14:11 ` [PATCH 3/3] include/uapi/linux/swab: Fix potentially missing __always_inline Pavo Banicevic
2021-07-28 13:49   ` Petr Vaněk

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