linux-kernel - Re: [PATCH] [v2] Kbuild: move to -std=gnu11

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Date:   Mon, 28 Feb 2022 14:19:11 +0100
From:   David Sterba <dsterba@...e.cz>
To:     Arnd Bergmann <arnd@...nel.org>
Cc:     Jani Nikula <jani.nikula@...ux.intel.com>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Masahiro Yamada <masahiroy@...nel.org>, llvm@...ts.linux.dev,
        Jonathan Corbet <corbet@....net>,
        Federico Vaga <federico.vaga@...a.pv.it>,
        Alex Shi <alexs@...nel.org>, Hu Haowen <src.res@...il.cn>,
        Michal Marek <michal.lkml@...kovi.net>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-doc-tw-discuss@...ts.sourceforge.net,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Intel Graphics <intel-gfx@...ts.freedesktop.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        greybus-dev@...ts.linaro.org, linux-staging@...ts.linux.dev,
        linux-btrfs <linux-btrfs@...r.kernel.org>
Subject: Re: [PATCH] [v2] Kbuild: move to -std=gnu11

On Mon, Feb 28, 2022 at 02:01:06PM +0100, Arnd Bergmann wrote:
> On Mon, Feb 28, 2022 at 1:36 PM Jani Nikula <jani.nikula@...ux.intel.com> wrote:
> > >
> > > One minor issue that remains is an added gcc warning for shifts of
> > > negative integers when building with -Werror, which happens with the
> > > 'make W=1' option, as well as for three drivers in the kernel that always
> > > enable -Werror, but it was only observed with the i915 driver so far.
> > > To be on the safe side, add -Wno-shift-negative-value to any -Wextra
> > > in a Makefile.
> >
> > Do you mean always enable -Wall and/or -Wextra instead of -Werror?
> >
> > We do use -Werror for our CI and development too, but it's hidden behind
> > a config option that depends on COMPILE_TEST=n to avoid any problems
> > with allmodconfig/allyesconfig.
> 
> What I meant here is that I'm adding -Wno-shift-negative-value to all
> four places in the kernel that already use -Wextra.
> 
> > For the future, makes me wonder if we couldn't have a way for drivers to
> > locally enable -Wall/-Wextra in a way that incorporates the exceptions
> > from kbuild instead of having to duplicate them.
> 
> I have an older patch series that does this, but it also does a few other
> things that I couldn't quite get right in the end with all combinations of
> compiler versions and warning levels, so I did not submit that.
> 
> What this allows is to have per-directory statements like
> 
> KBUILD_WARN1=1

We've added the individual warnings to the per-directory flags so it's a
bit more flexible than just enabling W=1. The idea is to add possibly
stricter warnings once we make sure it builds fine and does not
produce false reports. Extending W=1 in the same way would affect
everybody.