linux-kernel - Re: [PATCH] x86: fix early boot crash on gcc-10

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Date:   Tue, 17 Mar 2020 18:10:16 +0000
From:   Sergei Trofimovich <slyfox@...too.org>
To:     Jakub Jelinek <jakub@...hat.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andy Lutomirski <luto@...nel.org>, x86@...nel.org
Subject: Re: [PATCH] x86: fix early boot crash on gcc-10

On Tue, 17 Mar 2020 12:46:05 +0100
Jakub Jelinek <jakub@...hat.com> wrote:

> So, a few comments.
> 
> One thing I've noticed in the command line is that
> --param=allow-store-data-races=0
> got dropped.  That is fine, the parameter is gone, but it has been replaced
> in https://gcc.gnu.org/PR92046 by the
> -fno-allow-store-data-races
> option.  Like the param which defaulted to 0 and has been enabled only with
> -Ofast this option is also -fno-allow-store-data-races by default unless
> -Ofast, but if kernel wanted to be explicit or make sure not to introduce
> them even with -Ofast, I'd say it should:
>  # Tell gcc to never replace conditional load with a non-conditional one
>  KBUILD_CFLAGS   += $(call cc-option,--param=allow-store-data-races=0)
> +KBUILD_CFLAGS   += $(call cc-option,-fno-allow-store-data-races)
> in the toplevel Makefile.

Yeah, I noticed it yesterday as well and sent out exactly the same change:
    https://lkml.org/lkml/2020/3/16/1012
I also checked that flag does not change code generation on -O2 for smpboot.c

-- 

  Sergei