linux-kernel - Re: [PATCH] arm64/neon: Disable -Wincompatible-pointer-types when building with Clang

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Message-ID: <20190215185026.GE15084@fuggles.cambridge.arm.com>
Date:   Fri, 15 Feb 2019 18:50:26 +0000
From:   Will Deacon <will.deacon@....com>
To:     Nathan Chancellor <natechancellor@...il.com>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Mark Brown <broonie@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Kevin Hilman <khilman@...libre.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>
Subject: Re: [PATCH] arm64/neon: Disable -Wincompatible-pointer-types when
 building with Clang

On Thu, Feb 14, 2019 at 06:39:59PM -0700, Nathan Chancellor wrote:
> After commit cc9f8349cb33 ("arm64: crypto: add NEON accelerated XOR
> implementation"), Clang builds for arm64 started failing with the
> following error message.
> 
> arch/arm64/lib/xor-neon.c:58:28: error: incompatible pointer types
> assigning to 'const unsigned long *' from 'uint64_t *' (aka 'unsigned
> long long *') [-Werror,-Wincompatible-pointer-types]
>                 v3 = veorq_u64(vld1q_u64(dp1 +  6), vld1q_u64(dp2 + 6));
>                                          ^~~~~~~~
> /usr/lib/llvm-9/lib/clang/9.0.0/include/arm_neon.h:7538:47: note:
> expanded from macro 'vld1q_u64'
>   __ret = (uint64x2_t) __builtin_neon_vld1q_v(__p0, 51); \
>                                               ^~~~
> 
> There has been quite a bit of debate and triage that has gone into
> figuring out what the proper fix is, viewable at the link below, which
> is still ongoing. Ard suggested disabling this warning with Clang with a
> pragma so no neon code will have this type of error. While this is not
> at all an ideal solution, this build error is the only thing preventing
> KernelCI from having successful arm64 defconfig and allmodconfig builds
> on linux-next. Getting continuous integration running is more important
> so new warnings/errors or boot failures can be caught and fixed quickly.
> 
> Link: https://github.com/ClangBuiltLinux/linux/issues/283
> Suggested-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>
> Signed-off-by: Nathan Chancellor <natechancellor@...il.com>
> ---
>  arch/arm64/include/asm/neon-intrinsics.h | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/arch/arm64/include/asm/neon-intrinsics.h b/arch/arm64/include/asm/neon-intrinsics.h
> index 2ba6c6b9541f..71abfc7612b2 100644
> --- a/arch/arm64/include/asm/neon-intrinsics.h
> +++ b/arch/arm64/include/asm/neon-intrinsics.h
> @@ -36,4 +36,8 @@
>  #include <arm_neon.h>
>  #endif
>  
> +#ifdef CONFIG_CC_IS_CLANG
> +#pragma clang diagnostic ignored "-Wincompatible-pointer-types"
> +#endif

I'd like Ard's ack on this one, please.

Will