Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
From:   Thomas Gleixner <tglx@linutronix.de>
To:     Nick Desaulniers <ndesaulniers@google.com>,
        Arvind Sankar <nivedita@alum.mit.edu>
Cc:     "Paul E. McKenney" <paulmck@kernel.org>,
        Ingo Molnar <mingo@redhat.com>, Arnd Bergmann <arnd@arndb.de>,
        Borislav Petkov <bp@alien8.de>,
        "maintainer\:X86 ARCHITECTURE \(32-BIT AND 64-BIT\)" <x86@kernel.org>,
        "H. Peter Anvin" <hpa@zytor.com>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Zhenzhong Duan <zhenzhong.duan@oracle.com>,
        Kees Cook <keescook@chromium.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Juergen Gross <jgross@suse.com>,
        Andy Lutomirski <luto@kernel.org>,
        Andrew Cooper <andrew.cooper3@citrix.com>,
        LKML <linux-kernel@vger.kernel.org>,
        clang-built-linux <clang-built-linux@googlegroups.com>,
        Will Deacon <will@kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH] x86: work around clang IAS bug referencing __force_order
In-Reply-To: <CAKwvOdkoB+fT9tt7vgg1R6J-NEr77EWP5X8nFat_L-HvEzWGzA@mail.gmail.com>
References: <20200527135329.1172644-1-arnd@arndb.de> <878serh1b9.fsf@nanos.tec.linutronix.de> <CAKwvOdnOh3H3ga2qpTktywvcgfXW5QJaB7r4XMhigmDzLhDNeA@mail.gmail.com> <87h7t6tpye.fsf@nanos.tec.linutronix.de> <20200813173701.GC4295@paulmck-ThinkPad-P72> <20200813180933.GA532283@rani.riverdale.lan> <875z9dioll.fsf@nanos.tec.linutronix.de> <20200820130641.GA536306@rani.riverdale.lan> <87zh6ohm03.fsf@nanos.tec.linutronix.de> <20200821230435.GA56974@rani.riverdale.lan> <CAKwvOdkoB+fT9tt7vgg1R6J-NEr77EWP5X8nFat_L-HvEzWGzA@mail.gmail.com>
Date:   Sat, 22 Aug 2020 02:43:08 +0200
Message-ID: <87eenzqzmr.fsf@nanos.tec.linutronix.de>
MIME-Version: 1.0
Content-Type: text/plain
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Fri, Aug 21 2020 at 16:16, Nick Desaulniers wrote:
> On Fri, Aug 21, 2020 at 4:04 PM Arvind Sankar <nivedita@alum.mit.edu> wrote:
>> On Fri, Aug 21, 2020 at 02:37:48AM +0200, Thomas Gleixner wrote:
>> The gcc bug I linked to earlier is only fixed in gcc-6 onwards. Is that
>
> (based on https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82602#c14)
>
>> good enough to remove force_order? I can test gcc-4.9 and gcc-5 to check
>> if it would currently have any impact.

And that test tells you what exactly? That your particular build of
those compilers does not have the problem. A truly scientific approach.

> I think checking the disassemblies with a pre-gcc-6 would be good
> enough then; that bug isn't specific to this particular case.

What? I clearly want a statement from the GCC people that this won't
happen on pre gcc6 compilers and not just some 'works for me' statement
based on a randomly picked compiler build.

Thanks,

        tglx