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From:   Masahiro Yamada <masahiroy@kernel.org>
Date:   Fri, 15 Apr 2022 00:15:40 +0900
Message-ID: <CAK7LNARVKL4vCRHz5=_sW_oBpkpqhDu5Hp1hfG+Hnwqg-61HVA@mail.gmail.com>
Subject: Re: [PATCHv1] kbuild: support W=e to make build abort in case of warning
To:     Nicolas Schier <nicolas@fjasle.eu>
Cc:     Randy Dunlap <rdunlap@infradead.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Yann Droneaud <ydroneaud@opteya.com>,
        Michal Marek <michal.lkml@markovi.net>,
        Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>
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On Thu, Apr 14, 2022 at 10:19 PM Nicolas Schier <nicolas@fjasle.eu> wrote:
>
> P=C3=A5 l=C3=B8. 09. april 2022 kl. 10.47 +0000 skrev Masahiro Yamada:
> > On Sat, Apr 9, 2022 at 5:36 AM Randy Dunlap <rdunlap@infradead.org> Wro=
te:
> > >
> > >
> > >
> > > On 4/8/22 13:29, Nick Desaulniers wrote:
> > > > On Fri, Apr 8, 2022 at 4:06 AM Masahiro Yamada <masahiroy@kernel.or=
g> wrote:
> > > >>
> > > >> On Fri, Apr 8, 2022 at 5:46 PM Yann Droneaud <ydroneaud@opteya.com=
> wrote:
> > > >>>
> > > >>> When developing new code/feature, CONFIG_WERROR is most
> > > >>> often turned off, especially for people using make W=3D12 to
> > > >>> get more warnings.
> > > >>>
> > > >>> In such case, turning on -Werror temporarily would require
> > > >>> switching on CONFIG_WERROR in the configuration, building,
> > > >>> then switching off CONFIG_WERROR.
> > > >>>
> > > >>> For this use case, this patch introduces a new 'e' modifier
> > > >>> to W=3D as a short hand for KCFLAGS+=3D-Werror" so that -Werror
> > > >>> got added to the kernel (built-in) and modules' CFLAGS.
> > > >>>
> > > >>> Signed-off-by: Yann Droneaud <ydroneaud@opteya.com>
> > > >>> ---
> > > >>>  Makefile                   |  1 +
> > > >>>  scripts/Makefile.extrawarn | 13 +++++++++++--
> > > >>>  2 files changed, 12 insertions(+), 2 deletions(-)
> > > >>>
> > > >>> Changes since v0[0]:
> > > >>>
> > > >>>  - rebase on top of commit 64a91907c896 ("kbuild: refactor script=
s/Makefile.extrawarn")
> > > >>>  - document use case after commit 3fe617ccafd6 ("Enable '-Werror'=
 by default for all kernel builds")
> > > >>>
> > > >>> [0] https://lore.kernel.org/all/1422803720-14723-1-git-send-email=
-ydroneaud@opteya.com/
> > > >>
> > > >>
> > > >> I remembered the previous submission, I liked it, but I had lost i=
t.
> > > >>
> > > >> It seems already 7 years ago, (before I became the Kbuild maintain=
er).
> > > >> Thanks for coming back to this.
> > > >>
> > > >>
> > > >> I like this, but I will wait some time for review comments.
> > > >
> > > > Dunno, this seems pretty simple:
> > > >
> > > > $ ./scripts/config -e WERROR
> > > > $ make ... W=3D12
> > >
> > > Yeah, that's about what I was thinking too..
> >
> >
> >
> > But, you cannot change the .config
> > when you build external modules.
> >
> > "make W=3De" might be useful for people who strive to
> > keep their downstream modules warning-free.
> >
> >
> > W=3De is the same pattern.
> > I do not see much downside.
>
> If I set CONFIG_WERROR=3Dy on the make command line, I could have the
> same result, don't I?
>
>   make CONFIG_WERROR=3D1 ...
>
> no matter if in-tree or for external kernel modules.

Yes.

If you can change the kernel configuration,
you can enable CONFIG_WERROR.

To build external modules against the read-only
/lib/modules/$(uname -r)/build/,
it is not so feasible to change the .config file, though.


>
> Kind regards,
> Nicolas


--=20
Best Regards
Masahiro Yamada