linux-kernel - Re: [PATCH] kbuild: fix duplicated flags in DEBUG

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Date:   Wed, 3 Feb 2021 10:38:35 -0700
From:   Nathan Chancellor <nathan@...nel.org>
To:     Masahiro Yamada <masahiroy@...nel.org>
Cc:     linux-kbuild@...r.kernel.org, Sedat Dilek <sedat.dilek@...il.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Andi Kleen <andi@...stfloor.org>,
        Ian Rogers <irogers@...gle.com>,
        Mark Wielaard <mark@...mp.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Nathan Chancellor <natechancellor@...il.com>,
        clang-built-linux@...glegroups.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kbuild: fix duplicated flags in DEBUG_CFLAGS

On Wed, Feb 03, 2021 at 04:52:39PM +0900, Masahiro Yamada wrote:
> Sedat Dilek noticed duplicated debug flags passed when building C
> files with CONFIG_DEBUG_INFO.
> 
> I do not know much about his build environment, but yes, Kbuild
> recurses to the top Makefile with some build targets. For example,
> 'make CC=clang bindeb-pkg' reproduces the issue.
> 
> With commit 121c5d08d53c ("kbuild: Only add -fno-var-tracking-assignments
> for old GCC versions") applied, DEBUG_CFLAGS is now reset only when
> CONFIG_CC_IS_GCC=y.
> 
> Fix it to reset DEBUG_CFLAGS also when using Clang.
> 
> Fixes: 121c5d08d53c ("kbuild: Only add -fno-var-tracking-assignments for old GCC versions")
> Reported-by: Sedat Dilek <sedat.dilek@...il.com>
> Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>

Reviewed-by: Nathan Chancellor <nathan@...nel.org>

> ---
> 
>  Makefile | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/Makefile b/Makefile
> index 3d3f67b98ca2..769a38ee81b9 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -811,10 +811,12 @@ KBUILD_CFLAGS	+= -ftrivial-auto-var-init=zero
>  KBUILD_CFLAGS	+= -enable-trivial-auto-var-init-zero-knowing-it-will-be-removed-from-clang
>  endif
>  
> +DEBUG_CFLAGS	:=
> +
>  # Workaround for GCC versions < 5.0
>  # https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61801
>  ifdef CONFIG_CC_IS_GCC
> -DEBUG_CFLAGS	:= $(call cc-ifversion, -lt, 0500, $(call cc-option, -fno-var-tracking-assignments))
> +DEBUG_CFLAGS	+= $(call cc-ifversion, -lt, 0500, $(call cc-option, -fno-var-tracking-assignments))
>  endif
>  
>  ifdef CONFIG_DEBUG_INFO
> -- 
> 2.27.0
>