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From:   Masahiro Yamada <yamada.masahiro@socionext.com>
Date:   Wed, 22 Aug 2018 02:13:51 +0900
Message-ID: <CAK7LNAT39aFpgs0iAudYwpA4x6+B_8WZ0ftQ2Mff3-cTOd3Diw@mail.gmail.com>
Subject: Re: [PATCH] compiler-gcc: get back Clang build
To:     Joe Perches <joe@perches.com>
Cc:     Linus Torvalds <torvalds@linux-foundation.org>,
        Kees Cook <keescook@chromium.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Arnd Bergmann <arnd@arndb.de>,
        David Woodhouse <dwmw@amazon.co.uk>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Will Deacon <will.deacon@arm.com>,
        Geert Uytterhoeven <geert@linux-m68k.org>,
        Ingo Molnar <mingo@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>
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Hi Joe,


2018-08-21 19:39 GMT+09:00 Joe Perches <joe@perches.com>:
> On Tue, 2018-08-21 at 15:48 +0900, Masahiro Yamada wrote:
>> Commit cafa0010cd51 ("Raise the minimum required gcc version to 4.6")
>> missed the fact that <linux/compiler-gcc.h> is included by Clang
>> as well as by GCC.
>>
>> Clang actually defines __GNUC__, __GNUC_MINOR__, __GNUC_PATCHLEVEL__
>> and it looks like GCC 4.2.1.
>>
>>   $ scripts/gcc-version.sh -p clang
>>   040201
>
> Perhaps this would work, but I can't test it as
> my clang version doesn't otherwise build a defconfig
> and errors out with
>
> $ make CC=clang
> arch/x86/Makefile:179: *** Compiler lacks asm-goto support..  Stop.
>
> ---
>  include/linux/compiler-gcc.h | 17 +++++++++++++++++
>  1 file changed, 17 insertions(+)
>
> diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h
> index 3e70b7d4e9ed..3a06ad823fa4 100644
> --- a/include/linux/compiler-gcc.h
> +++ b/include/linux/compiler-gcc.h
> @@ -3,6 +3,23 @@
>  #error "Please don't include <linux/compiler-gcc.h> directly, include <linux/compiler.h> instead."
>  #endif
>
> +/*
> + * Override clang compiler version #defines
> + *
> + * compiler_types.h always #includes compiler-gcc.h before compiler-clang,h
> + * but clang sets these __GNUC version #defines to 4.2.1.
> + * This breaks the gcc minimum version of 4.6.0, so override the clang
> + * definitions to 4.6.0
> + */
> +#ifdef __clang__
> +    #undef __GNUC__
> +    #undef __GNUC_MINOR__
> +    #undef __GNUC_PATCHLEVEL__
> +    #define __GNUC__ 4
> +    #define __GNUC_MINOR__ 6
> +    #define __GNUC_PATCHLEVEL__ 0
> +#endif
> +
>

This patch does not work.

It only addresses the
"# error Sorry, your compiler is too old - please upgrade it." part.


Attributes unsupported by Clang
must be ifdef'ed  out.

Otherwise, you will see lots of unknown attribute warnings.

-- 
Best Regards
Masahiro Yamada