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From:   Andy Lutomirski <luto@kernel.org>
Date:   Thu, 25 Oct 2018 17:09:48 -0700
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Subject: Re: [v3 03/12] x86/fsgsbase/64: Add intrinsics/macros for FSGSBASE instructions
To:     Linus Torvalds <torvalds@linux-foundation.org>
Cc:     Andrew Lutomirski <luto@kernel.org>,
        Andi Kleen <ak@linux.intel.com>,
        "Bae, Chang Seok" <chang.seok.bae@intel.com>,
        Ingo Molnar <mingo@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        "Metzger, Markus T" <markus.t.metzger@intel.com>,
        "Ravi V. Shankar" <ravi.v.shankar@intel.com>,
        LKML <linux-kernel@vger.kernel.org>
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On Thu, Oct 25, 2018 at 4:31 PM Linus Torvalds
<torvalds@linux-foundation.org> wrote:
>
> On Thu, Oct 25, 2018 at 4:14 PM Andy Lutomirski <luto@kernel.org> wrote:
> >
> > On Wed, Oct 24, 2018 at 12:21 PM Andi Kleen <ak@linux.intel.com> wrote:
> > >
> > > BTW the other option would be to update the min-binutils requirement
> > > to 2.21 (currently it is 2.20) and then write it directly without .byte.
> > > I believe 2.21 added support for these instructions.
> > >
> > > (It's only a binutils requirement, don't need gcc support)
> >
> > I'd personally be fine with this.  Linus? Thomas? Ingo?
>
> I always vote for "require modern tools" as long as it doesn't cause problems.
>
> binutils-2.21 is something like seven years old by now, but the real
> issue would be what versions distros are actually shipping. I don't
> want people to have to build their own binutils just to build a
> kernel.
>
> It's usually some ancient enterprise distro that is stuck on old
> versions. Anybody have any idea?
>

With some basic Googling:

CentOS 6 is binutils 2.23.  CentOS 5 is EOL.  RHEL 5 has "extended
life", which means that it's officially zombified and paying customers
can still download (unsupported) packages.

SLES 11 is binutils 2.19, which is already unsupported.  SLES 12 is 2.24.

So I would guess we're okay and we can bump the requirement to 2.21.