linux-kernel - Re: [PATCH v2] kbuild: Enable -Wtautological-compare

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Date:   Sun, 29 Mar 2020 20:31:26 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     Nathan Chancellor <natechancellor@...il.com>
Cc:     Michal Marek <michal.lkml@...kovi.net>,
        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>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>
Subject: Re: [PATCH v2] kbuild: Enable -Wtautological-compare

On Fri, Mar 27, 2020 at 4:42 AM Nathan Chancellor
<natechancellor@...il.com> wrote:
>
> Currently, we disable -Wtautological-compare, which in turn disables a
> bunch of more specific tautological comparison warnings that are useful
> for the kernel such as -Wtautological-bitwise-compare. See clang's
> documentation below for the other warnings that are suppressed by
> -Wtautological-compare. Now that all of the major/noisy warnings have
> been fixed, enable -Wtautological-compare so that more issues can be
> caught at build time by various continuous integration setups.
>
> -Wtautological-constant-out-of-range-compare is kept disabled under a
> normal build but visible at W=1 because there are places in the kernel
> where a constant or variable size can change based on the kernel
> configuration. These are not fixed in a clean/concise way and the ones
> I have audited so far appear to be harmless. It is not a subgroup but
> rather just one warning so we do not lose out on much coverage by
> default.
>
> Link: https://github.com/ClangBuiltLinux/linux/issues/488
> Link: http://releases.llvm.org/10.0.0/tools/clang/docs/DiagnosticsReference.html#wtautological-compare
> Link: https://bugs.llvm.org/show_bug.cgi?id=42666
> Signed-off-by: Nathan Chancellor <natechancellor@...il.com>
> ---
>
> v1 -> v2: https://lore.kernel.org/lkml/20200219045423.54190-7-natechancellor@gmail.com/
>
> * Expand commit message a bit by adding more reasoning behind change.
> * Disable -Wtautological-constant-out-of-range-compare under a normal
>   build but allow it to show up at W=1 for easy auditing.
>
> I hope this can be accepted for 5.7. There are two warnings that I see
> still across a bunch of allyesconfig/allmodconfig builds that have
> patches sent but not accepted. I will ping them today.
>
> * https://lore.kernel.org/lkml/20191023002014.22571-1-natechancellor@gmail.com/
> * https://lore.kernel.org/lkml/20200220051011.26113-1-natechancellor@gmail.com/


OK, I will queue this up and send it to Linus
in the second week of MW.

I hope all warnings will be fixed by that time.



-- 
Best Regards
Masahiro Yamada