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From:   Nick Desaulniers <ndesaulniers@google.com>
Date:   Wed, 6 Feb 2019 09:36:55 -0800
Message-ID: <CAKwvOdm=dqScCDVTgQ71i0wtBSqezEzLr69Pxp3bZJFs+_mXsQ@mail.gmail.com>
Subject: Re: [PATCH] kbuild, LLVMLinux: Don't suppress format warnings
To:     Jon Flatley <jflat@chromium.org>
Cc:     Nathan Chancellor <natechancellor@gmail.com>,
        Masahiro Yamada <yamada.masahiro@socionext.com>,
        Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Michal Marek <michal.lkml@markovi.net>
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On Wed, Feb 6, 2019 at 9:32 AM Jon Flatley <jflat@chromium.org> wrote:
>
> On Wed, Feb 6, 2019 at 8:45 AM Nathan Chancellor
> <natechancellor@gmail.com> wrote:
> >
> > On Tue, Feb 05, 2019 at 05:26:05PM +0900, Masahiro Yamada wrote:
> > > On Sat, Feb 2, 2019 at 6:10 AM <jflat@chromium.org> wrote:
> > > >
> > > > From: Jon Flatley <jflat@chromium.org>
> > > >
> > > > gcc produces format warnings that clang suppresses. To keep behavior
> > > > consistent between gcc and clang, don't suppress format warnings in
> > > > clang.
> > > >
> > > > Signed-off-by: Jon Flatley <jflat@chromium.org>
> > > > ---
> > >
> > > Applied to linux-kbuild.
> > > Thanks.
> > >
> > >
> >
> > Hi Jon and Masahiro,
> >
> > Just as a heads up, this introduces a ton of warnings (duh). Isn't the
> > typical plan behind turning on warnings that were disabled to build with
> > 'W=', fix them all, then turn them on so as not to pollute the build?
> >
> > Log file: https://gist.github.com/443db156e56cd3c0f6b21d9d77728d80

Oh boy, that's a lot.  Too many to fix quickly IMO.

> >
> > Note a big chunk of them come from one scnprintf call in
> > include/linux/usb/wusb.h but still, there are many other warnings that
> > make quite a bit of noise. Some seem relatively easy to fix, which I
> > suppose I will try to tackle soon.
> >
> > Thanks,
> > Nathan
> >
>
> Hi Nathan,
>
> This was definitely not my intention.
> I noticed the added warnings this morning and was considering calling
> for a revert on this patch.
>
> The intent was to match the behavior of gcc, as it has -Wformat enabled.
> It was rather naive of me to assume the behavior of -Wformat would be
> the same in both gcc and clang.
> Indeed, it seems gcc is more permissive about what format
> substitutions it allows.
>
> For example passing int to the "%hu" format specifier is fine in gcc
> under -Wformat but produces a warning in clang.
> Maybe this was the motivation for adding -Wno-format to clang in the
> first place.

Sorry, I'm late to this thread.  What is it reverting; who authored
the original patch? Was it mka@chromium.org?

> This difference is puzzling to me, and I wonder if it's by design.

Probably; internally let's sync up with the Clang devs to understand
this difference more.

>
> Considering the whole point of this patch was to sync up this behavior
> between gcc and clang I am OK with reverting this.

Is this patch in -next, or has it already hit mainline?  I think it's
better to revert, then start upstreaming fixes, then re-land it once
we're warning free.

-- 
Thanks,
~Nick Desaulniers