linux-kernel - Re: [PATCH] Makefile.extrawarn: re-enable -Wformat for clang; take 2

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Date:   Sun, 4 Sep 2022 03:22:17 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Joe Perches <joe@...ches.com>,
        Nathan Chancellor <nathan@...nel.org>,
        "Sudip Mukherjee (Codethink)" <sudipm.mukherjee@...il.com>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        clang-built-linux <llvm@...ts.linux.dev>,
        Justin Stitt <jstitt007@...il.com>,
        Youngmin Nam <youngmin.nam@...sung.com>
Subject: Re: [PATCH] Makefile.extrawarn: re-enable -Wformat for clang; take 2

On Fri, Sep 2, 2022 at 2:59 AM Nick Desaulniers <ndesaulniers@...gle.com> wrote:
>
> -Wformat was recently re-enabled for builds with clang, then quickly
> re-disabled, due to concerns stemming from the frequency of default
> argument promotion related warning instances.
>
> commit 258fafcd0683 ("Makefile.extrawarn: re-enable -Wformat for clang")
> commit 21f9c8a13bb2 ("Revert "Makefile.extrawarn: re-enable -Wformat for clang"")
>
> ISO WG14 has ratified N2562 to address default argument promotion
> explicitly for printf, as part of the upcoming ISO C2X standard.
>
> The behavior of clang was changed in clang-16 to not warn for the cited
> cases in all language modes.
>
> Add a version check, so that users of clang-16 now get the full effect
> of -Wformat. For older clang versions, re-enable flags under the
> -Wformat group that way users still get some useful checks related to
> format strings, without noisy default argument promotion warnings. I
> intentionally omitted -Wformat-y2k and -Wformat-security from being
> re-enabled, which are also part of -Wformat in clang-16.
>
> Link: https://github.com/ClangBuiltLinux/linux/issues/378
> Link: https://github.com/llvm/llvm-project/issues/57102
> Link: https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2562.pdf
> Suggested-by: Justin Stitt <jstitt007@...il.com>
> Suggested-by: Nathan Chancellor <nathan@...nel.org>
> Suggested-by: Youngmin Nam <youngmin.nam@...sung.com>
> Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.com>
> ---
> Linus, I figured I'd send this to you to see whether you'd prefer to
> apply it, or let it "ride the trains" up through the kbuild tree? I do
> have another series I'm working on to improve the compiler version
> checks
> <https://lore.kernel.org/llvm/20220831184408.2778264-4-ndesaulniers@google.com/>
> where I can/will improve the checks used here, but I'm also interested in
> having something that might backport cleanly to stable.

Linus was addressed, so I just reviewed it.

Reviewed-by: Masahiro Yamada <masahiroy@...nel.org>


-- 
Best Regards
Masahiro Yamada