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From:   Arnd Bergmann <arnd@kernel.org>
Date:   Mon, 25 Jul 2022 16:35:38 +0200
Message-ID: <CAK8P3a2ZfEr+4OWWteZHpDYGw8U0dQgMfF_OFwQDEtY=GaTfQA@mail.gmail.com>
Subject: Re: [linux-stable-rc:linux-5.15.y 6874/8723] arch/arm/lib/xor-neon.c:30:2:
 warning: This code requires at least version 4.6 of GCC
To:     Ard Biesheuvel <ardb@kernel.org>
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "Jason A. Donenfeld" <Jason@zx2c4.com>,
        kernel test robot <lkp@intel.com>,
        "Justin M. Forbes" <jforbes@fedoraproject.org>,
        clang-built-linux <llvm@lists.linux.dev>,
        kbuild-all@lists.01.org,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        "Jason A. Donenfeld" <zx2c4@kernel.org>
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On Mon, Jul 25, 2022 at 2:55 PM Arnd Bergmann <arnd@kernel.org> wrote:

> The other easy workaround would be to just turn off the xor-neon code
> when building with clang, e.g. using this Makefile hack:
>
> diff --git a/arch/arm/lib/Makefile b/arch/arm/lib/Makefile
> index 6d2ba454f25b..8e4fe6421dd2 100644
> --- a/arch/arm/lib/Makefile
> +++ b/arch/arm/lib/Makefile
> @@ -43,8 +43,10 @@ endif
>  $(obj)/csumpartialcopy.o:      $(obj)/csumpartialcopygeneric.S
>  $(obj)/csumpartialcopyuser.o:  $(obj)/csumpartialcopygeneric.S
>
> +ifdef CONFIG_CC_IS_CLANG
>  ifeq ($(CONFIG_KERNEL_MODE_NEON),y)
>    NEON_FLAGS                   := -march=armv7-a -mfloat-abi=softfp -mfpu=neon
>    CFLAGS_xor-neon.o            += $(NEON_FLAGS)
>    obj-$(CONFIG_XOR_BLOCKS)     += xor-neon.o
>  endif
> +endif

Nevermind, this does not actually work. Just turning off the warning
is probably best then, as actually disabling this code would still
be invasive not do much beyond saving a little bit of kernel .text size.

        Arnd