linux-kernel - Re: [PATCH 3/4] kbuild: re-order the code to not parse unnecessary variables

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Date:   Mon, 9 Oct 2017 15:03:24 -0700
From:   Doug Anderson <dianders@...omium.org>
To:     Masahiro Yamada <yamada.masahiro@...ionext.com>
Cc:     Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Sam Ravnborg <sam@...nborg.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/4] kbuild: re-order the code to not parse unnecessary variables

Hi,

On Tue, Oct 3, 2017 at 8:56 PM, Masahiro Yamada
<yamada.masahiro@...ionext.com> wrote:
> The top Makefile is divided into some sections such as mixed targets,
> config targets, build targets, etc.
>
> When we build mixed targets, Kbuild just invokes submake to process
> them one by one.  In this case, compiler-related variables like CC,
> KBUILD_CFLAGS, etc. are unneeded.
>
> Check what kind of targets we are building first, then parse necessary
> variables for building them.
>
> Signed-off-by: Masahiro Yamada <yamada.masahiro@...ionext.com>
> ---
>
>  Makefile | 233 ++++++++++++++++++++++++++++++++-------------------------------
>  1 file changed, 118 insertions(+), 115 deletions(-)

I'm even further outside my comfort zone with this big of a change,
but I will say that as far as I can tell this seems like a good
change.  If it were me I'd have probably broken it up into several
tinier changes that were each massively easy to check/verify, but
presumably for those who know the Makefile better then rolling them
together is fine.  ;)

I're spent some time reviewing this (not tons--maybe an hour or so),
but IMHO I don't know this well enough to add a Reviewed-by tag.


> diff --git a/Makefile b/Makefile
> index 39a7c03..a4fd682 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -186,15 +186,6 @@ ifeq ("$(origin M)", "command line")
>    KBUILD_EXTMOD := $(M)
>  endif
>
> -# If building an external module we do not care about the all: rule
> -# but instead _all depend on modules
> -PHONY += all
> -ifeq ($(KBUILD_EXTMOD),)
> -_all: all
> -else
> -_all: modules
> -endif
> -
>  ifeq ($(KBUILD_SRC),)
>          # building in the source tree
>          srctree := .
> @@ -206,6 +197,9 @@ else
>                  srctree := $(KBUILD_SRC)
>          endif
>  endif
> +
> +export KBUILD_CHECKSRC KBUILD_EXTMOD KBUILD_SRC

The old Makefile also used to export KBUILD_SRC, but I'm not sure why.
Shouldn't this be implicit because KBUILD_SRC always comes from a
command line parameter or environment variable?


-Doug