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From:   Nick Desaulniers <ndesaulniers@google.com>
Date:   Mon, 16 Aug 2021 13:06:13 -0700
Message-ID: <CAKwvOdnc-GAHOQtjrjFzc6GzCLR35rQ6uVAenLLKBkEqws9Tbw@mail.gmail.com>
Subject: Re: [PATCH] Makefile: remove stale cc-option checks
To:     Masahiro Yamada <masahiroy@kernel.org>
Cc:     Michal Marek <michal.lkml@markovi.net>,
        Nathan Chancellor <nathan@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        "Paul E. McKenney" <paulmck@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Miguel Ojeda <ojeda@kernel.org>,
        Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
        Vitor Massaru Iha <vitor@massaru.org>,
        Sedat Dilek <sedat.dilek@gmail.com>,
        Daniel Latypov <dlatypov@google.com>,
        Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        clang-built-linux <clang-built-linux@googlegroups.com>
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On Fri, Aug 13, 2021 at 6:43 PM Masahiro Yamada <masahiroy@kernel.org> wrote:
>
> On Wed, Aug 11, 2021 at 5:42 AM Nick Desaulniers
> <ndesaulniers@google.com> wrote:
> >
> > diff --git a/Makefile b/Makefile
> > index 027fdf2a14fe..3e3fb4affba1 100644
> > --- a/Makefile
> > +++ b/Makefile
> > @@ -798,7 +801,7 @@ include/config/auto.conf:
> >  endif # may-sync-config
> >  endif # need-config
> >
> > -KBUILD_CFLAGS  += $(call cc-option,-fno-delete-null-pointer-checks,)
> > +KBUILD_CFLAGS  += -fno-delete-null-pointer-checks
> >  KBUILD_CFLAGS  += $(call cc-disable-warning,frame-address,)
> >  KBUILD_CFLAGS  += $(call cc-disable-warning, format-truncation)
> >  KBUILD_CFLAGS  += $(call cc-disable-warning, format-overflow)
> > @@ -844,17 +847,17 @@ KBUILD_RUSTFLAGS += -Copt-level=z
> >  endif
> >
> >  # Tell gcc to never replace conditional load with a non-conditional one
> > -KBUILD_CFLAGS  += $(call cc-option,--param=allow-store-data-races=0)
> > +ifdef CONFIG_CC_IS_GCC
>
>
> Can you insert a comment here?
>
> # GCC 10 renamed --param=allow-store-data-races=0 to --allow-store-data-races
>
>
> It will remind us of dropping this conditional
> in the (long long distant) future.
>
>
>
>
> > +KBUILD_CFLAGS  += $(call cc-option,--allow-store-data-races,--param=allow-store-data-races=0)
> >  KBUILD_CFLAGS  += $(call cc-option,-fno-allow-store-data-races)
> > +endif

So it looks like `-fallow-store-data-races` was also supported. Reading through
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97309
https://gcc.gnu.org/wiki/Atomic/GCCMM/ExecutiveSummary
it seems that the default is not to allow "store data races." So I
should not be adding `--allow-store-data-races` or
`-fallow-store-data-races`; so this just should be the existing test,
with a comment that it can be removed once gcc-10+ is the minimum.
Will update that in v2.
-- 
Thanks,
~Nick Desaulniers