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

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Date:   Mon, 29 Jul 2019 09:04:12 -0700
From:   Nathan Chancellor <natechancellor@...il.com>
To:     Masahiro Yamada <yamada.masahiro@...ionext.com>
Cc:     linux-kbuild@...r.kernel.org, Stephen Boyd <swboyd@...omium.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        stable@...r.kernel.org, Michal Marek <michal.lkml@...kovi.net>,
        clang-built-linux@...glegroups.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kbuild: initialize CLANG_FLAGS correctly in the top
 Makefile

On Mon, Jul 29, 2019 at 06:15:17PM +0900, Masahiro Yamada 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+
> Signed-off-by: Masahiro Yamada <yamada.masahiro@...ionext.com>

Reviewed-by: Nathan Chancellor <natechancellor@...il.com>