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

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Date:   Mon, 16 May 2022 07:19:53 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     Arnd Bergmann <arnd@...nel.org>, 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>,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-doc-tw-discuss@...ts.sourceforge.net,
        linux-arm-kernel@...ts.infradead.org,
        intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        greybus-dev@...ts.linaro.org, linux-staging@...ts.linux.dev,
        linux-btrfs@...r.kernel.org
Subject: Re: [greybus-dev] Re: [PATCH] [v2] Kbuild: move to -std=gnu11

On 5/16/22 06:31, Greg KH wrote:
> On Mon, May 16, 2022 at 06:10:23AM -0700, Guenter Roeck wrote:
>> On Mon, Feb 28, 2022 at 11:27:43AM +0100, Arnd Bergmann wrote:
>>> From: Arnd Bergmann <arnd@...db.de>
>>>
>>> During a patch discussion, Linus brought up the option of changing
>>> the C standard version from gnu89 to gnu99, which allows using variable
>>> declaration inside of a for() loop. While the C99, C11 and later standards
>>> introduce many other features, most of these are already available in
>>> gnu89 as GNU extensions as well.
>>
>> The downside is that backporting affected patches to older kernel branches
>> now fails with error messages such as
>>
>> mm/kfence/core.c: In function ‘kfence_init_pool’:
>> mm/kfence/core.c:595:2: error: ‘for’ loop initial declarations are only allowed in C99 or C11 mode
>>
>> Just something to keep in mind when writing patches.
> 
> I just ran across this very issue on this commit.  It's an easy fixup
> for 5.17.y to make this work, so I did that in my tree.  If this gets to
> be too much, we might need to reconsider adding c11 to older stable
> kernels.
> 

I think I'll do just that for ChromeOS; I don't want to have to deal
with the backports, and we are using recent compilers anyway.

Guenter