From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:58719) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1dFzXQ-0005GR-2p for qemu-devel@nongnu.org; Wed, 31 May 2017 05:03:33 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1dFzXL-000700-RX for qemu-devel@nongnu.org; Wed, 31 May 2017 05:03:32 -0400 Received: from mx1.redhat.com ([209.132.183.28]:50790) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1dFzXL-0006yd-LY for qemu-devel@nongnu.org; Wed, 31 May 2017 05:03:27 -0400 Date: Wed, 31 May 2017 10:03:22 +0100 From: "Richard W.M. Jones" Message-ID: <20170531090322.GD31999@redhat.com> References: <1c8f4f4e-65f7-2d12-a391-08781fea651c@landley.net> <20170529101413.GN16511@redhat.com> <7e4d7d67-3312-2d2a-ab64-8c0f171d9118@landley.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <7e4d7d67-3312-2d2a-ab64-8c0f171d9118@landley.net> Subject: Re: [Qemu-devel] Commit b2a575a1c652 broke i486 support. List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Rob Landley Cc: Thomas Huth , qemu-devel@nongnu.org, Marc =?iso-8859-1?Q?Mar=ED?= , Paolo Bonzini On Tue, May 30, 2017 at 02:05:15PM -0500, Rob Landley wrote: > On 05/29/2017 05:14 AM, Richard W.M. Jones wrote: > > I see in the disassembly use of cmovne (new in Pentium Pro) and > > bswap (new in 486). > > [http://cse.unl.edu/~goddard/Courses/CSCE351/IntelArchitecture/InstructionSetSummary.pdf] > > > > The cmovne instruction is generated by the compiler (GCC in my case), > > > > The following patch removes the cmovne instruction, so it should work > > on 486 (although I didn't test it). It's not possible to remove bswap > > without surgery on the inline assembler. > > Is there any way to make it just _not_ load the option rom for -cpu 486? > It ran fine before that thing went in... Well it ran, but it was very slow. The DMA method can be literally orders of magnitude faster. Does adding the flag I suggested help? Rich. -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming and virtualization blog: http://rwmj.wordpress.com virt-builder quickly builds VMs from scratch http://libguestfs.org/virt-builder.1.html