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:     Arnd Bergmann <arnd@arndb.de>, Ingo Molnar <mingo@redhat.com>,
        Borislav Petkov <bp@alien8.de>, x86@kernel.org
Cc:     Arnd Bergmann <arnd@arndb.de>, "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>,
        linux-kernel@vger.kernel.org, clang-built-linux@googlegroups.com
Subject: Re: [PATCH] x86: work around clang IAS bug referencing __force_order
In-Reply-To: <20200527135329.1172644-1-arnd@arndb.de>
References: <20200527135329.1172644-1-arnd@arndb.de>
Date:   Fri, 07 Aug 2020 00:11:38 +0200
Message-ID: <878serh1b9.fsf@nanos.tec.linutronix.de>
MIME-Version: 1.0
Content-Type: text/plain
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Arnd Bergmann <arnd@arndb.de> writes:
> When using the clang integrated assembler, we get a reference
> to __force_order that should normally get ignored in a few
> rare cases:
>
> ERROR: modpost: "__force_order" [drivers/cpufreq/powernow-k6.ko] undefined!
>
> Add a 'static' definition so any file in which this happens can
> have a local copy.

That's a horrible hack.

And the only reason why it does not trigger -Wunused-variable warnings
all over the place is because it's "referenced" in unused inline
functions and then optimized out along with the unused inlines.

>   * It is not referenced from the code, but GCC < 5 with -fPIE would fail
>   * due to an undefined symbol. Define it to make these ancient GCCs
>   work.

Bah, we really should have moved straight to GCC5 instead of upping it
just to 4.9

> + *
> + * Clang sometimes fails to kill the reference to the dummy variable, so
> + * provide an actual copy.

Can that compiler be fixed instead?

Aside of that is there a reason to make this 'static' thing wrapped in
#ifdeffery? A quick check with GCC8.3 just works. But maybe 4.9 gets
unhappy. Can't say due to: -ENOANCIENTCOMPILER :)

Thanks,

        tglx