Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Tue, 11 Dec 2018 00:58:09 +0100
From:   Pavel Machek <pavel@ucw.cz>
To:     Linus Torvalds <torvalds@linux-foundation.org>
Cc:     Steven Rostedt <rostedt@goodmis.org>,
        Andy Lutomirski <luto@amacapital.net>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Andrew Lutomirski <luto@kernel.org>,
        the arch/x86 maintainers <x86@kernel.org>,
        Linux List Kernel Mailing <linux-kernel@vger.kernel.org>,
        Ard Biesheuvel <ard.biesheuvel@linaro.org>,
        Ingo Molnar <mingo@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>, mhiramat@kernel.org,
        jbaron@akamai.com, Jiri Kosina <jkosina@suse.cz>,
        David.Laight@aculab.com, bp@alien8.de, julia@ni.com,
        jeyu@kernel.org, Peter Anvin <hpa@zytor.com>
Subject: Re: [PATCH v2 4/4] x86/static_call: Add inline static call
 implementation for x86-64
Message-ID: <20181210235809.GB22352@amd>
References: <20181129121307.12393c57@gandalf.local.home>
 <CAHk-=wik5AfDs7qqjGHQ5vRBYkV8K6tFmPna3PdbwdzVwPGTsg@mail.gmail.com>
 <20181129124404.2fe55dd0@gandalf.local.home>
 <CAHk-=wgnZobye-KNaBVO-SdqX-5Xkz+i=aJ_kOFZ4RpZFT0HqQ@mail.gmail.com>
 <20181129125857.75c55b96@gandalf.local.home>
 <CAHk-=wigLUgxDM6Dq2aS7efduffratP976Ggmpv4Ev4EOrJxyA@mail.gmail.com>
 <20181129134725.6d86ade6@gandalf.local.home>
 <CAHk-=wgbnQs4fpuHqT1jLkDnKcvTGS5EN8m=qy7oUE5n_fhOig@mail.gmail.com>
 <CAHk-=wjN=sow0F-UtA6DtHHT_CNUV7wYVe3cQ4E8GPp4LN32+Q@mail.gmail.com>
 <CAHk-=whxtKjkDbvA4EK0aU+FpqALyW+p79_nuPy99PjYFnkbvQ@mail.gmail.com>
MIME-Version: 1.0
Content-Type: multipart/signed; micalg=pgp-sha1;
        protocol="application/pgp-signature"; boundary="JP+T4n/bALQSJXh8"
Content-Disposition: inline
In-Reply-To: <CAHk-=whxtKjkDbvA4EK0aU+FpqALyW+p79_nuPy99PjYFnkbvQ@mail.gmail.com>
User-Agent: Mutt/1.5.23 (2014-03-12)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk


--JP+T4n/bALQSJXh8
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
Content-Transfer-Encoding: quoted-printable

On Thu 2018-11-29 11:11:50, Linus Torvalds wrote:
> On Thu, Nov 29, 2018 at 11:08 AM Linus Torvalds
> <torvalds@linux-foundation.org> wrote:
> >
> > What you can do then is basically add a single-byte prefix to the
> > "call" instruction that does nothing (say, cs override), and then
> > replace *that* with a 'int3' instruction.
>=20
> Hmm. the segment prefixes are documented as being "reserved" for
> branch instructions. I *think* that means just conditional branches
> (Intel at one point used the prefixes for static prediction
> information), not "call", but who knows..
>=20
> It might be better to use an empty REX prefix on x86-64 or something like=
 that.

It might be easiest to use plain old NOP, no? :-).
									Pavel
--=20
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blo=
g.html

--JP+T4n/bALQSJXh8
Content-Type: application/pgp-signature; name="signature.asc"
Content-Description: Digital signature

-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1

iEYEARECAAYFAlwO/ZEACgkQMOfwapXb+vJgBQCgqbl0bzR1o2UMcqonrUj27dbe
5A8An0++oQbTeDDo6wxa0cJu+VcUqiTE
=W9W+
-----END PGP SIGNATURE-----

--JP+T4n/bALQSJXh8--