netdev - Re: [PATCH net-next v2 1/2] Makefile.extrawarn: Add symbol for W=1 warnings for today

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Date:   Sun, 11 Oct 2020 22:03:45 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        netdev <netdev@...r.kernel.org>,
        David Miller <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Rohit Maheshwari <rohitm@...lsio.com>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>
Subject: Re: [PATCH net-next v2 1/2] Makefile.extrawarn: Add symbol for W=1
 warnings for today

On Tue, Oct 6, 2020 at 6:08 AM Andrew Lunn <andrew@...n.ch> wrote:
>
> > It depends a lot on what portion of the kernel gets enabled for W=1.
> >
> > As long as it's only drivers that are actively maintained, and they
> > make up a fairly small portion of all code, it should not be a problem
> > to find someone to fix useful warnings.
>
> Well, drivers/net/ethernet is around 1.5M LOC. The tree as a whole is
> just short of 23M LOC. So i guess that is a small portion of all the
> code.
>
>         Andrew

I am not a big fan of KBUILD_CFLAGS_W1_<timestamp>
since it is ugly.

I'd like to start with adding individual flags
like drivers/gpu/drm/i915/Makefile, and see
how difficult it would be to maintain it.

One drawback of your approach is that
you cannot set KBUILD_CFLAGS_W1_20200930
until you eliminate all the warnings in the
sub-directory in interest.
(i.e. all or nothing approach)

At best, you can only work out from 'old -> new' order
because KBUILD_CFLAGS_W1_20200326 is a suer-set of
KBUILD_CFLAGS_W1_20190907, which is a suer-set of
KBUILD_CFLAGS_W1_20190617 ...

If you add flags individually, you can start with
low-hanging fruits, or ones with higher priority
as Arnd mentions about -Wmissing-{declaration,prototypes}.

For example, you might be able to set
'subdir-ccflags-y += -Wmissing-declarations'
to drivers/net/Makefile, while
'subdir-ccflags-y += -Wunused-but-set-variable'
stays in drivers/net/ethernet/Makefile.

--
Best Regards
Masahiro Yamada