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bh=a1zqHJq3h3H4AWGO98Tj35F2wWnZ3D9g1ubNoHn99Sk=; b=VmnJ+sju3ecIVRso42foi1mUYzAsPcLvQRNRJB+ttQ1i7zM+4UDQum9sNzhQJE9NEfpvwT 9feURSImbdJz8bAwk8DYmlcSFbUFUossF1tmpNoYj2T2mCoFI7J0Z/xtLx4Z26XHe4DHBJ FK8LyUMPw+5F8n1Ugp36R7DxBorxFdU= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-375-7qhaHXhBNh-UguyCWCrMFg-1; Fri, 23 Apr 2021 05:00:41 -0400 X-MC-Unique: 7qhaHXhBNh-UguyCWCrMFg-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 46A26343A0; Fri, 23 Apr 2021 09:00:40 +0000 (UTC) Received: from redhat.com (ovpn-112-17.ams2.redhat.com [10.36.112.17]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 608C72921F; Fri, 23 Apr 2021 09:00:37 +0000 (UTC) Date: Fri, 23 Apr 2021 10:00:34 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Thomas Huth Subject: Re: Compiling the s390-ccw bios with clang (was: Re: s390-ccw: warning: writing 1 byte into a region of size 0) Message-ID: References: <20210422155238.kak7tl3xnup5vod7@steredhat> <20210423064001.fjouibdcwadtgijy@steredhat> <8abfb851-a5d2-8608-fe96-2eb3014adb96@redhat.com> <20210423100708.262eeaf0.cohuck@redhat.com> <856dfa3f-e7ee-b88e-47e4-96d39dba20c3@redhat.com> <44304a9e-9907-31ec-53a2-44bc7123c688@redhat.com> MIME-Version: 1.0 In-Reply-To: <44304a9e-9907-31ec-53a2-44bc7123c688@redhat.com> User-Agent: Mutt/2.0.5 (2021-01-21) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=berrange@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=216.205.24.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable autolearn_force=no X-Spam_action: no action 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 , Janosch Frank , Cornelia Huck , Richard Henderson , qemu-devel , Christian Borntraeger , qemu-s390x , Philippe =?utf-8?Q?Mathieu-Daud=C3=A9?= , Stefano Garzarella Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Fri, Apr 23, 2021 at 10:52:35AM +0200, Thomas Huth wrote: > On 23/04/2021 10.47, Daniel P. Berrangé wrote: > > On Fri, Apr 23, 2021 at 10:22:28AM +0200, Thomas Huth wrote: > > > On 23/04/2021 10.07, Cornelia Huck wrote: > > > > On Fri, 23 Apr 2021 09:57:08 +0200 > > > > Thomas Huth wrote: > > > > > > > > > On 23/04/2021 08.52, Christian Borntraeger wrote: > > > > > [...] > > > > > > We can of course discuss if we compile the BIOS for z10 instead of z900. TCG > > > > > > in the mean time can handle up to z13 and z10 is now also 13 years old. > > > > > > > > > > I'd really like to see us supporting Clang in the s390-ccw bios, too, since > > > > > it provides additional useful compiler warnings ... but switching the -mz900 > > > > > to -mz10 here also means that we could not boot VMs anymore that use a CPU > > > > > that is older than the z10... > > > > > > > > We could still boot a kernel/initrd directly, couldn't we? > > > > > > Yes, but that will certainly require some documentation effort to make it > > > clear to the users that they need to use "-kernel" in case they want to run > > > an older guest... > > > > > > > > Is anybody still using such old CPUs? Should we maybe deprecate all CPUs > > > > > that are older than the z10 in QEMU? Alternatively, we could try to detect > > > > > Clang in the Makefile, and only use -mz10 in that case and continue to use > > > > > -mz900 in the other case...? > > > > > > > > So, the issue with clang is that it compiles to at least a z10, right? > > > > > > Right, Clang does not support anything that is older than a z10. > > > > IIUC, according to wikipedia > > > > - z10 series was introduced in 2008 > > - z900 series was introduced in 2000 > > > > Even the z10 is well older than the oldest OS platform we support. > > > > Though I presume people keep mainframes deployed for longer than commodity > > x86 hardware, it doesn't seem too unreasonable to say z10 is the oldest > > we'll support. > > Well, we're talking about *guest* support here. So with that argumentation, > we could also remove support for old CPUs like "486" or "SandyBridge" from > qemu-system-x86_64 ... should we maybe also start the deprecation there? Oh true, I forgot it would have implications for usability of the -cpu flag choices, I was only thinking about the guest OS, as you can sitll use a guest OS compiled for z900 even if the BIOS is targetting z10. So need to compile BIOS with z900 is effectively equivalent to the need to compile x86 BIOS for oldest generation CPU. Downstream distros have the choice to limit what CPUs they wish to support, but upstream if QEMU targets legacy emulation use cases, then we want to support all CPUs. Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|