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[170.10.129.124]) by mx.google.com with ESMTPS id q12-20020a05620a024c00b00728811980bbsi6848421qkn.532.2023.03.06.06.06.36 for (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 06 Mar 2023 06:06:37 -0800 (PST) Received-SPF: pass (google.com: domain of berrange@redhat.com designates 170.10.129.124 as permitted sender) client-ip=170.10.129.124; Authentication-Results: mx.google.com; dkim=pass header.i=@redhat.com header.s=mimecast20190719 header.b=ZJLEAGre; spf=pass (google.com: domain of berrange@redhat.com designates 170.10.129.124 as permitted sender) smtp.mailfrom=berrange@redhat.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1678111596; h=from:from:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=voMt6AB+9qNIUfz/3mjHZ4ciEx34KDCiHB56iJwYfX4=; b=ZJLEAGrecUxCYD9MEVc+hcAxuVCN+ILXZj8/vNCusrpnpKwcQJzJcTyENCEbq9iT6pRyqI +sr34wAKSC5RVHK82t7uk7hjbejbq/m4udSpy8sF73C9k1qldVwTvtEfTBskf4L+/yvgrP mTZReEIyTsClRNNxc+82P1DbfkhY8Qg= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-669-l5ZckLzFOV6jvPPgyotFqw-1; Mon, 06 Mar 2023 09:06:33 -0500 X-MC-Unique: l5ZckLzFOV6jvPPgyotFqw-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.rdu2.redhat.com [10.11.54.8]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 7F118830D44; Mon, 6 Mar 2023 14:06:14 +0000 (UTC) Received: from redhat.com (unknown [10.33.36.53]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 1C159C1602A; Mon, 6 Mar 2023 14:06:10 +0000 (UTC) Date: Mon, 6 Mar 2023 14:06:08 +0000 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Thomas Huth Cc: qemu-devel@nongnu.org, Peter Maydell , Paolo Bonzini , Markus Armbruster , Alex =?utf-8?Q?Benn=C3=A9e?= , qemu-arm@nongnu.org, Maxim Levitsky , libvir-list@redhat.com, Richard Henderson , xen-devel@lists.xenproject.org, Reinoud Zandijk , Wilfred Mallawa , John Paul Adrian Glaubitz Subject: Re: [PATCH v4 2/5] docs/about/deprecated: Deprecate the qemu-system-i386 binary Message-ID: Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= References: <20230306084658.29709-1-thuth@redhat.com> <20230306084658.29709-3-thuth@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/2.2.9 (2022-11-12) X-Scanned-By: MIMEDefang 3.1 on 10.11.54.8 X-TUID: Zt/wEJNA1X6h On Mon, Mar 06, 2023 at 02:48:16PM +0100, Thomas Huth wrote: > On 06/03/2023 10.27, Daniel P. Berrangé wrote: > > On Mon, Mar 06, 2023 at 09:46:55AM +0100, Thomas Huth wrote: > > > [...] If a 32-bit CPU guest > > > +environment should be enforced, you can switch off the "long mode" CPU > > > +flag, e.g. with ``-cpu max,lm=off``. > > > > I had the idea to check this today and this is not quite sufficient, > [...] > > A further difference is that qemy-system-i686 does not appear to enable > > the 'syscall' flag, but I've not figured out where that difference is > > coming from in the code. > > I think I just spotted this by accident in target/i386/cpu.c > around line 637: > > #ifdef TARGET_X86_64 > #define TCG_EXT2_X86_64_FEATURES (CPUID_EXT2_SYSCALL | CPUID_EXT2_LM) > #else > #define TCG_EXT2_X86_64_FEATURES 0 > #endif Hmm, so right now the difference between qemu-system-i386 and qemu-system-x86_64 is based on compile time conditionals. So we have the burden of building everything twice and also a burden of testing everything twice. If we eliminate qemu-system-i386 we get rid of our own burden, but users/mgmt apps need to adapt to force qemu-system-x86_64 to present a 32-bit system. What about if we had qemu-system-i386 be a hardlink to qemu-system-x86_64, and then changed behaviour based off the executed binary name ? ie if running qemu-system-i386, we could present a 32-bit CPU by default. We eliminate all of our double compilation burden still. We still have extra testing burden, but it is in a fairly narrow area, so does not imply x2 the testing burden just $small-percentage extra testing ? That would means apps/users would not need to change at all, but we still get most of the win we're after on the QEMU side Essentially #ifdef TARGET_X86_64 would be change 'if (is_64bit) {...}' in a handful of places, with 'bool is_64bit' initialized in main() from argv[0] ? With 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 :|