From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 31913 invoked by alias); 20 Oct 2008 01:14:01 -0000 Received: (qmail 31904 invoked by uid 22791); 20 Oct 2008 01:14:01 -0000 X-Spam-Check-By: sourceware.org Received: from smtp-outbound-1.vmware.com (HELO smtp-outbound-1.vmware.com) (65.115.85.69) by sourceware.org (qpsmtpd/0.31) with ESMTP; Mon, 20 Oct 2008 01:13:22 +0000 Received: from mailhost2.vmware.com (mailhost2.vmware.com [10.16.67.167]) by smtp-outbound-1.vmware.com (Postfix) with ESMTP id 637661302B for ; Sun, 19 Oct 2008 18:13:21 -0700 (PDT) Received: from [10.20.92.59] (promb-2s-dhcp59.eng.vmware.com [10.20.92.59]) by mailhost2.vmware.com (Postfix) with ESMTP id 333428E568 for ; Sun, 19 Oct 2008 18:13:21 -0700 (PDT) Message-ID: <48FBDA34.6020104@vmware.com> Date: Mon, 20 Oct 2008 01:14:00 -0000 From: Michael Snyder User-Agent: Thunderbird 1.5.0.12 (X11/20080411) MIME-Version: 1.0 To: gdb@sourceware.org Subject: [discuss] semantics, "replay debugging" vs. "reverse debugging" Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-IsSubscribed: yes Mailing-List: contact gdb-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: gdb-owner@sourceware.org X-SW-Source: 2008-10/txt/msg00071.txt.bz2 Just to make sure we're all on the same page, I'm gonna state what I believe is true, and invite discussion or contradiction. Replay debugging --> ability to record an execution sequence and "play it back" (repeat it) with some degree of determinism. Reverse debugging --> ability to make the inferior process "back up" to a previous state, eg. reverse step and reverse continue-to-breakpoint. They're related but not identical. One could theoretically have one without the other, although in practice all presently existing reverse-debug targets (that I know of) are implemented by using record and replay. One could have reverse without record/replay if, for instance, one had a machine architecture where all instructions were reversable, ie. the machine itself could reverse-execute an instruction. And an example of a record/replay implementation without reverse debugging capability would be Michael Chastain's (circa 1999) implementation of Linux system-call based record and replay, which could deterministically replay a recorded program execution, but did not have reverse-step or reverse-continue-to-breakpoint.