From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:42106) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1UdxwP-0004Je-Bu for qemu-devel@nongnu.org; Sun, 19 May 2013 03:22:03 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1UdxwO-0000S7-Ag for qemu-devel@nongnu.org; Sun, 19 May 2013 03:22:01 -0400 Received: from mail-lb0-f181.google.com ([209.85.217.181]:57536) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1UdxwO-0000Ry-3V for qemu-devel@nongnu.org; Sun, 19 May 2013 03:22:00 -0400 Received: by mail-lb0-f181.google.com with SMTP id w20so5260730lbh.12 for ; Sun, 19 May 2013 00:21:58 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <1368938253.2611.4@driftwood> References: <519667A7.9010902@greensocs.com> <1368938253.2611.4@driftwood> From: Peter Maydell Date: Sun, 19 May 2013 08:21:38 +0100 Message-ID: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Subject: Re: [Qemu-devel] [RFC] reverse execution. List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Rob Landley Cc: Blue Swirl , Mark Burton , qemu-devel , =?UTF-8?B?S09OUkFEIEZyw6lkw6lyaWM=?= On 19 May 2013 05:37, Rob Landley wrote: > On 05/17/2013 12:23:51 PM, KONRAD Fr=C3=A9d=C3=A9ric wrote: >> It appeared that the replay is not deterministic even with icount: > You're aware that reverse execution means you have the "come from" proble= m, > right? (The opposite of goto.) > > You literally _can't_ figure out your control flow by running the code > backwards. It's equivalent to solving the halting problem. The best you c= an > do is log and replay. Yes, of course -- 'reverse execution' is just the usual phrase for the user-visible effect. However if your *forwards* replay isn't deterministic then it all goes pear-shaped, which is what Fred is complaining about. -- PMM