linux-kernel - RE: [PATCH] x86: work around clang IAS bug referencing __force

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Message-ID: <016a02d1019f4d0eba67e37d3be2d74d@AcuMS.aculab.com>
Date:   Thu, 13 Aug 2020 08:49:14 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Nick Desaulniers' <ndesaulniers@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>
CC:     Arnd Bergmann <arnd@...db.de>, Borislav Petkov <bp@...en8.de>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Zhenzhong Duan <zhenzhong.duan@...cle.com>,
        Kees Cook <keescook@...omium.org>,
        "Peter Zijlstra" <peterz@...radead.org>,
        Juergen Gross <jgross@...e.com>,
        "Andy Lutomirski" <luto@...nel.org>,
        Andrew Cooper <andrew.cooper3@...rix.com>,
        LKML <linux-kernel@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>
Subject: RE: [PATCH] x86: work around clang IAS bug referencing __force_order

From: Nick Desaulniers
> Sent: 13 August 2020 01:13
> 
> On Thu, Aug 6, 2020 at 3:11 PM Thomas Gleixner <tglx@...utronix.de> wrote:
> >
> > Arnd Bergmann <arnd@...db.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.
> 
> Agreed.  And static means everyone gets their own copy, rather than
> sharing one memory address.  I guess no one actually writes to it, so
> it doesn't really matter, but __force_order just seems so strange to
> me.

It could be changed to use a symbol that the linker script already defines.
However it does look like a workaround for a broken version of gcc.

	David

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