linux-kernel - Re: [PATCH v3 1/2] kbuild: refactor scripts/Makefile.extrawarn

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Date:   Wed, 4 Sep 2019 15:40:50 -0700
From:   Nathan Chancellor <natechancellor@...il.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Sedat Dilek <sedat.dilek@...il.com>,
        Michal Marek <michal.lkml@...kovi.net>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 1/2] kbuild: refactor scripts/Makefile.extrawarn

On Wed, Sep 04, 2019 at 11:46:45PM +0200, Arnd Bergmann wrote:
> On Sat, Aug 31, 2019 at 6:26 PM Masahiro Yamada
> <yamada.masahiro@...ionext.com> wrote:
> 
> > +# Some diagnostics enabled by default are noisy.
> > +# Suppress them by using -Wno... except for W=1.
> > +
> >  ifdef CONFIG_CC_IS_CLANG
> >  KBUILD_CFLAGS += -Wno-initializer-overrides
> >  KBUILD_CFLAGS += -Wno-format
> >  KBUILD_CFLAGS += -Wno-sign-compare
> >  KBUILD_CFLAGS += -Wno-format-zero-length
> >  endif
> 
> FWIW, I just found out I missed a bug that clang failed to warn about
> because of the  -Wno-format. Apparently gcc warns only about type
> mismatches that result in incompatible calling conventions (e.g.
> int vs int64_t) but not smaller types (int, short) that get converted to an
> int anyway. Passing -Wno-format turns both off.
> 
>       Arnd

Hi Arnd,

This has been fixed in clang 10.0.0 but this areas has not been updated
as nobody has sent a patch yet:

https://github.com/ClangBuiltLinux/linux/issues/378#issuecomment-524411147

Cheers,
Nathan