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

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Message-ID: <CAK8P3a0CTmtUq+Uba2S3D7wjSstew2M+LfzZoOcKdKK9cfXO9A@mail.gmail.com>
Date:   Mon, 28 Feb 2022 12:37:37 +0100
From:   Arnd Bergmann <arnd@...nel.org>
To:     Mark Rutland <mark.rutland@....com>
Cc:     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>,
        Marco Elver <elver@...gle.com>
Subject: Re: [PATCH] [v2] Kbuild: move to -std=gnu11

On Mon, Feb 28, 2022 at 12:25 PM Mark Rutland <mark.rutland@....com> wrote:
> On Mon, Feb 28, 2022 at 11:27:43AM +0100, Arnd Bergmann wrote:
> >
> > Nathan Chancellor reported an additional -Wdeclaration-after-statement
> > warning that appears in a system header on arm, this still needs a
> > workaround.
>
> FWIW, I had a go at moving to c99 a few weeks ago (to be able to use
> for-loop-declarations in some concurrency primitives), and when I tried, I also
> saw declaration-after-statement warnings when building modpost.c, which is easy
> enough to fix:
>
>   https://git.kernel.org/pub/scm/linux/kernel/git/mark/linux.git/commit/?h=treewide/gnu99&id=505775bd6fd0bc1883f3271f826963066bbdc194

I think the KBUILD_USERCFLAGS portion and the modpost.c fix for it
make sense regardless of the -std=gnu11 change, but your change
to KBUILD_CFLAGS is not actually needed because the warning is
already enabled there -- gnu89 allows intermingled declarations since
gcc-3.4, so the warning flag was added during early 2.6.x kernels.

       Arnd