linux-kernel - Re: [greybus-dev] [PATCH] Kbuild: remove -std=gnu89 from compiler arguments

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Message-ID: <72ff1b04-4f37-9851-a6e6-aded72b46c83@linaro.org>
Date:   Sun, 27 Feb 2022 17:57:52 -0600
From:   Alex Elder <elder@...aro.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Arnd Bergmann <arnd@...nel.org>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>,
        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-gfx <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: [greybus-dev] [PATCH] Kbuild: remove -std=gnu89 from compiler
 arguments

On 2/27/22 5:11 PM, Linus Torvalds wrote:
> On Sun, Feb 27, 2022 at 3:04 PM Alex Elder <elder@...aro.org> wrote:
>>
>> Glancing at the Greybus code, I don't believe there's any
>> reason it needs to shift a negative value.  Such warnings
>> could be fixed by making certain variables unsigned, for
>> example.
> 
> As mentioned in the original thread, making things unsigned actually
> is likely to introduce bugs and make things worse.

Understood.  What I meant is that the shifts were producing
single-bit masks from plain int values that range from 0 to 10
or something (in a for loop).  Looking again though, that it's
not so simple.  Regardless, your point about the warning is
good and I won't plan to "fix" this.

Thanks.

					-Alex
> 
> The warning is simply bogus, and the fact that it was enabled by
> -Wextra in gcc for std=gnu99 and up was a mistake that looks likely to
> be fixed in gcc.
> 
> So don't try to "fix" the code to make any possible warnings go away.
> You may just make things worse.
> 
> (That is often true in general for the more esoteric warnings, but in
> this case it's just painfully more obvious).
> 
>                Linus