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

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Date:   Wed, 4 Sep 2019 23:46:45 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Masahiro Yamada <yamada.masahiro@...ionext.com>
Cc:     Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nathan Chancellor <natechancellor@...il.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 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