From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D0245C4360C for ; Mon, 30 Sep 2019 09:27:02 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id A3C9A21721 for ; Mon, 30 Sep 2019 09:27:02 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A3C9A21721 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:47882 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iErxN-0007n8-M1 for qemu-devel@archiver.kernel.org; Mon, 30 Sep 2019 05:27:01 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:60277) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iErwH-0006ft-EA for qemu-devel@nongnu.org; Mon, 30 Sep 2019 05:25:54 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1iErwG-0001c5-2S for qemu-devel@nongnu.org; Mon, 30 Sep 2019 05:25:53 -0400 Received: from mx1.redhat.com ([209.132.183.28]:34130) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1iErwB-0001Zy-Ew; Mon, 30 Sep 2019 05:25:47 -0400 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 4B85818CB8F9; Mon, 30 Sep 2019 09:25:46 +0000 (UTC) Received: from redhat.com (unknown [10.42.17.55]) by smtp.corp.redhat.com (Postfix) with ESMTPS id C73D01001B33; Mon, 30 Sep 2019 09:25:44 +0000 (UTC) Date: Mon, 30 Sep 2019 10:25:42 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Richard Henderson Subject: Re: [RFC PATCH] configure: deprecate 32 bit build hosts Message-ID: <20190930092519.GB11996@redhat.com> References: <20190925233013.6449-1-alex.bennee@linaro.org> <4512b61a-ed82-e628-88e5-f44ef87c2b50@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <4512b61a-ed82-e628-88e5-f44ef87c2b50@linaro.org> User-Agent: Mutt/1.12.1 (2019-06-15) X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.6.2 (mx1.redhat.com [10.5.110.63]); Mon, 30 Sep 2019 09:25:46 +0000 (UTC) Content-Transfer-Encoding: quoted-printable X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 209.132.183.28 X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Cc: Peter Maydell , "open list:RISC-V" , QEMU Developers , qemu-discuss , qemu-s390x , qemu-arm , qemu-ppc@nongnu.org, Alex =?utf-8?Q?Benn=C3=A9e?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Thu, Sep 26, 2019 at 10:11:05AM -0700, Richard Henderson wrote: > On 9/26/19 12:50 AM, Peter Maydell wrote: > > On Thu, 26 Sep 2019 at 00:31, Alex Benn=C3=A9e wrote: > >> > >> The 32 bit hosts are already a second class citizen especially with > >> support for running 64 bit guests under TCG. We are also limited by > >> testing as actual working 32 bit machines are getting quite rare in > >> developers personal menageries. For TCG supporting newer types like > >> Int128 is a lot harder with 32 bit calling conventions compared to > >> their larger bit sized cousins. Fundamentally address space is the > >> most useful thing for the translator to have even for a 32 bit guest= a > >> 32 bit host is quite constrained. > >> > >> As far as I'm aware 32 bit KVM users are even less numerous. Even > >> ILP32 doesn't make much sense given the address space QEMU needs to > >> manage. > >=20 > > For KVM we should wait until the kernel chooses to drop support, > > I think. >=20 > Agreed. I think this discussion should be more about TCG. >=20 > >> @@ -745,19 +744,22 @@ case "$cpu" in > >> ;; > >> armv*b|armv*l|arm) > >> cpu=3D"arm" > >> - supported_cpu=3D"yes" > >> ;; > >=20 > > I'll leave others to voice opinions about their architectures, > > but I still have 32-bit arm in my test set for builds, and > > I'm pretty sure we have users (raspi users, for a start). >=20 > I'd really like to know what raspi users might be using qemu for. Depe= nding on > that answer, perhaps it would be sufficient for arm32 tcg to only suppo= rt > 32-bit guests. I asked on the Fedora development lists for feedback on the idea of dropping QEMU 32-bit host support https://lists.fedoraproject.org/archives/list/devel@lists.fedoraproject= .org/thread/TPAVIC6YANGP2NK4RUOP7OCIOIFIOV3A/ The response was rather underwhealming to say the least, with only one person explicitly expressing a desire for QEMU to keep 32-bit host support for armv7l. The main interesting thing I learnt was that even with 64-bit Raspberry Pi hardware, it can be desirable to run 32-bit Raspberry Pi supporting distro, supposedly for performance benefits. > For context, the discussion that Alex and I were having was about int12= 8_t, and > how to support that directly in tcg (especially to/from helpers), and h= ow that > might be vastly easier if we didn't have to consider 32-bit hosts. I know nothing about TCG internals, but Is it viable to implement int128_= t support only in 64-bit host, leaving 32-bit hosts without it ? Or is this really a blocking item that is holding back 64-bit host features. Regards, Daniel --=20 |: https://berrange.com -o- https://www.flickr.com/photos/dberran= ge :| |: https://libvirt.org -o- https://fstop138.berrange.c= om :| |: https://entangle-photo.org -o- https://www.instagram.com/dberran= ge :|