linux-kernel - Re: [PATCH] kbuild: fix compile time regression

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Date:   Fri, 17 Mar 2017 02:41:17 +0900
From:   Masahiro Yamada <yamada.masahiro@...ionext.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Michal Marek <mmarek@...e.com>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] kbuild: fix compile time regression

2017-03-16 23:31 GMT+09:00 Arnd Bergmann <arnd@...db.de>:
> I noticed that a patch I did causes the time for a clean rebuild to
> go up significantly, from 13 to 18 seconds on ARM defconfig, and
> in the worst case forcing a rebuild of every file each time.
>
> The fix is very simple, using a ':=' assignment instead of '='
> to force the cc-disable-warning call to only be evaluated once
> instead of every time.
>
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>  Makefile | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/Makefile b/Makefile
> index 3a964fa3a787..e7d4d20deb4e 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -381,7 +381,7 @@ LDFLAGS_MODULE  =
>  CFLAGS_KERNEL  =
>  AFLAGS_KERNEL  =
>  LDFLAGS_vmlinux =
> -CFLAGS_GCOV    = -fprofile-arcs -ftest-coverage -fno-tree-loop-im $(call cc-disable-warning,maybe-uninitialized,)
> +CFLAGS_GCOV    := -fprofile-arcs -ftest-coverage -fno-tree-loop-im $(call cc-disable-warning,maybe-uninitialized,)
>  CFLAGS_KCOV    := $(call cc-option,-fsanitize-coverage=trace-pc,)
>
>  ifeq ($(COMPILER),clang)
> --


Squashed into the first patch.


-- 
Best Regards
Masahiro Yamada