linux-kernel - Re: [PATCH] kbuild: initialize CLANG_FLAGS correctly in the top Makefile

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Message-ID: <CAK7LNASjXdMJG5OVz4qhyGHHLGd0uZO9ifH_iqkUqYxKD+Xn2g@mail.gmail.com>
Date:   Mon, 29 Jul 2019 18:38:59 +0900
From:   Masahiro Yamada <yamada.masahiro@...ionext.com>
To:     Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>
Cc:     Stephen Boyd <swboyd@...omium.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nathan Chancellor <natechancellor@...il.com>,
        stable <stable@...r.kernel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] kbuild: initialize CLANG_FLAGS correctly in the top Makefile

On Mon, Jul 29, 2019 at 6:16 PM Masahiro Yamada
<yamada.masahiro@...ionext.com> wrote:
>
> CLANG_FLAGS is initialized by the following line:
>
>   CLANG_FLAGS     := --target=$(notdir $(CROSS_COMPILE:%-=%))
>
> ..., which is run only when CROSS_COMPILE is set.
>
> Some build targets (bindeb-pkg etc.) recurse to the top Makefile.
>
> When you build the kernel with Clang but without CROSS_COMPILE,
> the same compiler flags such as -no-integrated-as are accumulated
> into CLANG_FLAGS.
>
> If you run 'make CC=clang' and then 'make CC=clang bindeb-pkg',
> Kbuild will recompile everything needlessly due to the build command
> change.
>
> Fix this by correctly initializing CLANG_FLAGS.
>
> Fixes: 238bcbc4e07f ("kbuild: consolidate Clang compiler flags")
> Cc: <stable@...r.kernel.org> # v4.20+

This should be v5.0+

> Signed-off-by: Masahiro Yamada <yamada.masahiro@...ionext.com>
> ---


-- 
Best Regards
Masahiro Yamada