linux-kernel - Re: + kbuild-disable-wformat-truncation-warnings-by-default.patch added to -mm tree

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Date:   Thu, 20 Jul 2017 10:17:12 +0200
From:   gregkh <gregkh@...uxfoundation.org>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        mm-commits@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        stable <stable@...r.kernel.org>
Subject: Re: + kbuild-disable-wformat-truncation-warnings-by-default.patch
 added to -mm tree

On Thu, Jul 20, 2017 at 09:24:21AM +0200, Arnd Bergmann wrote:
> On Wed, Jul 19, 2017 at 11:50 PM,  <akpm@...ux-foundation.org> wrote:
> > ------------------------------------------------------
> > From: Arnd Bergmann <arnd@...db.de>
> > Subject: kbuild: disable -Wformat-truncation warnings by default
> >
> > With x86 allmodconfig, we currently get 233 -Wformat-truncation warnings,
> > which makes the entire warnings rather useless.
> >
> > This turns off the warning by default, unless we specify W=1 or higher
> >
> > Link: http://lkml.kernel.org/r/20170714120720.906842-2-arnd@arndb.de
> > Signed-off-by: Arnd Bergmann <arnd@...db.de>
> > Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
> > ---
> >
> >  scripts/Makefile.extrawarn |    3 +++
> >  1 file changed, 3 insertions(+)
> >
> > diff -puN scripts/Makefile.extrawarn~kbuild-disable-wformat-truncation-warnings-by-default scripts/Makefile.extrawarn
> > --- a/scripts/Makefile.extrawarn~kbuild-disable-wformat-truncation-warnings-by-default
> > +++ a/scripts/Makefile.extrawarn
> > @@ -67,5 +67,8 @@ KBUILD_CFLAGS += $(call cc-disable-warni
> >  KBUILD_CFLAGS += $(call cc-disable-warning, sign-compare)
> >  KBUILD_CFLAGS += $(call cc-disable-warning, format-zero-length)
> >  KBUILD_CFLAGS += $(call cc-disable-warning, uninitialized)
> > +else
> > +# noisy gcc-7 warnings
> > +KBUILD_CFLAGS += $(call cc-option,-Wformat-truncation=0)
> >  endif
> >  endif
> 
> Hi Andrew, Linus, Greg,
> 
> I noticed that Linus has made a similar patch in 4.13-rc1, commit bd664f6b3e37
> ("disable new gcc-7.1.1 warnings for now"), and it completely disables three
> warnings (format-truncation, format-overflow and int-in-bool-context).
> 
> Obviously there is no point in having both, so let's talk about what we
> want for 4.13, stable-backports and for future kernels, I'll then send those
> patches. Here is my first suggestion:
> 
> - enable all three warnings with "make W=1" in 4.13, but leave them
>   disabled by default.
> - backport Linus' patch, plus the follow-up for W=1 to stable kernels,
>   to allow stable kernels to build cleanly

I don't care which of these, I'll take whatever is in Linus's tree.
And I'll go backport that patch now as I'm getting annoyed by the
warnings at the moment...

> - backport the patches that address any other gcc-7 warnings, as
>   well as those that are not obvious false-positives to stable kernels

I'll do that as well, as I notice them go by.

> - In 4.14+, use my version above and address all int-in-bool-context
>   and format-overflow warnings, but only use -Wformat-truncation
>   with make W=1.

I don't really care about this, as long as we are not forced to do
"silly things" like some of the patches seemed to do :)

thanks,

greg k-h