linux-kernel - Re: [PATCH 1/2] x86: Do not add -falign flags unconditionally for clang

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Date:   Thu, 16 Sep 2021 19:18:42 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Nathan Chancellor <nathan@...nel.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
        Masahiro Yamada <masahiroy@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        linux-kernel@...r.kernel.org, linux-kbuild@...r.kernel.org,
        clang-built-linux@...glegroups.com, llvm@...ts.linux.dev,
        kernel test robot <lkp@...el.com>
Subject: Re: [PATCH 1/2] x86: Do not add -falign flags unconditionally for
 clang

On Mon, Aug 23, 2021 at 07:26:39PM -0700, Nathan Chancellor wrote:

A couple of nitpicks:

> Subject: [PATCH 1/2] x86: Do not add -falign flags unconditionally for clang

Make that prefix into "x86/build: " 

> clang does not support -falign-jumps and only recently gained support
> for -falign-loops. When one of the configuration options that adds these
> flags is enabled, clang warns and all cc-{disable-warning,option} that
> follow fail because -Werror gets added to test for the presence of this
> warning:
> 
> clang-14: warning: optimization flag '-falign-jumps=0' is not supported
> [-Wignored-optimization-argument]
> 
> To resolve this, add a couple of cc-option calls when building with
> clang; gcc has supported these options since 3.2 so there is no point in
> testing for their support. -falign-functions was implemented in clang-7,
> -falign-loops was implemented in clang-14, and -falign-jumps has not
> been implemented yet.
> 
> Link: https://lore.kernel.org/r/YSQE2f5teuvKLkON@Ryzen-9-3900X.localdomain/

Also, there should be a second Link: tag which points to this mail
thread so that we can find it later, when we dig for the "why we did
that" question :)

I.e.,

Link: 20210824022640.2170859-2-nathan@...nel.org

> Reported-by: kernel test robot <lkp@...el.com>
> Signed-off-by: Nathan Chancellor <nathan@...nel.org>
> ---
>  arch/x86/Makefile_32.cpu | 12 +++++++++---
>  1 file changed, 9 insertions(+), 3 deletions(-)

with that:

Acked-by: Borislav Petkov <bp@...e.de>

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette