From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from eggs.gnu.org ([2001:4830:134:3::10]:52727)
	by lists.gnu.org with esmtp (Exim 4.71)
	(envelope-from <rth7680@gmail.com>) id 1ZFyiw-0000OA-2c
	for qemu-devel@nongnu.org; Fri, 17 Jul 2015 02:02:18 -0400
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <rth7680@gmail.com>) id 1ZFyis-0005du-1Q
	for qemu-devel@nongnu.org; Fri, 17 Jul 2015 02:02:17 -0400
Received: from mail-wg0-x22b.google.com ([2a00:1450:400c:c00::22b]:34867)
	by eggs.gnu.org with esmtp (Exim 4.71)
	(envelope-from <rth7680@gmail.com>) id 1ZFyir-0005di-Qa
	for qemu-devel@nongnu.org; Fri, 17 Jul 2015 02:02:13 -0400
Received: by wgav7 with SMTP id v7so8496965wga.2
	for <qemu-devel@nongnu.org>; Thu, 16 Jul 2015 23:02:13 -0700 (PDT)
Sender: Richard Henderson <rth7680@gmail.com>
References: <1437081950-7206-1-git-send-email-rth@twiddle.net>
	<1437081950-7206-3-git-send-email-rth@twiddle.net>
	<CAFEAcA-9+DTX2ES5bmczv1Cr_U+hHxWBZ7Go8=4Y=0XngqtH1g@mail.gmail.com>
From: Richard Henderson <rth@twiddle.net>
Message-ID: <55A89A61.4070005@twiddle.net>
Date: Fri, 17 Jul 2015 07:02:09 +0100
MIME-Version: 1.0
In-Reply-To: <CAFEAcA-9+DTX2ES5bmczv1Cr_U+hHxWBZ7Go8=4Y=0XngqtH1g@mail.gmail.com>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Transfer-Encoding: 7bit
Subject: Re: [Qemu-devel] [PATCH 2/2] tcg/i386: Reserve register for
 guest_base if a segment isn't available
List-Id: <qemu-devel.nongnu.org>
List-Unsubscribe: <https://lists.nongnu.org/mailman/options/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>
List-Archive: <http://lists.nongnu.org/archive/html/qemu-devel>
List-Post: <mailto:qemu-devel@nongnu.org>
List-Help: <mailto:qemu-devel-request@nongnu.org?subject=help>
List-Subscribe: <https://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
To: Peter Maydell <peter.maydell@linaro.org>
Cc: Leon Alrae <leon.alrae@imgtec.com>, QEMU Developers <qemu-devel@nongnu.org>, Aurelien Jarno <aurelien@aurel32.net>

On 07/17/2015 02:33 AM, Peter Maydell wrote:
> On 16 July 2015 at 22:25, Richard Henderson <rth@twiddle.net> wrote:
>> This saves 2 insns and 10 bytes from the implementation of
>> each memory operation.
>
> Do we have an idea of which platforms/configs don't let
> us have a segment register for guest_base?

We've only bothered to fill in code for Linux so far.

These days we should probably probe for fsgsbase insns and use those.  Though I 
don't know how many of the various operating systems enable that...


r~