linux-kernel - Re: [PATCH] kbuild: Enable -Wimplicit-fallthrough for clang 14.0.0+

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Message-ID: <CAHk-=wgFXOf9OUh3+vmWjhp1PC47RVsUkL0NszBxSWhbGzx4tw@mail.gmail.com>
Date:   Mon, 16 Aug 2021 18:37:57 -1000
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Nathan Chancellor <nathan@...nel.org>
Cc:     "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>
Subject: Re: [PATCH] kbuild: Enable -Wimplicit-fallthrough for clang 14.0.0+

On Mon, Aug 16, 2021 at 6:20 PM Nathan Chancellor <nathan@...nel.org> wrote:
>
> Additionally, there should be some time for the CI systems to update
> their clang-14 builds, as the recent 0day report shows.

What?

No, the 0day report shows that the patch is buggy, and that the

  ifeq ($(shell test $(CONFIG_CLANG_VERSION) -ge 140000; echo $$?),0)

clearly doesn't work at all, since the flag is enabled on those
systems with old clang versions.

Alternatively, the test works, but the 140000 version is not enough.

So no. This patch is simply completely wrong, and doesn't fix the
problem with Clang's buggy -Wimplicit-fallthrough flag.

              Linus