From nobody Fri Oct 10 13:08:46 2025 Delivered-To: importer@patchew.org Received-SPF: pass (zoho.com: domain of gnu.org designates 208.118.235.17 as permitted sender) client-ip=208.118.235.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Authentication-Results: mx.zohomail.com; spf=pass (zoho.com: domain of gnu.org designates 208.118.235.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org Return-Path: Received: from lists.gnu.org (lists.gnu.org [208.118.235.17]) by mx.zohomail.com with SMTPS id 1545133088257110.18026029408577; Tue, 18 Dec 2018 03:38:08 -0800 (PST) Received: from localhost ([::1]:53314 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1gZDhO-0007NR-S5 for importer@patchew.org; Tue, 18 Dec 2018 06:38:06 -0500 Received: from eggs.gnu.org ([2001:4830:134:3::10]:46996) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1gZDSM-0003Nv-TL for qemu-devel@nongnu.org; Tue, 18 Dec 2018 06:22:36 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1gZDSL-0006UT-2C for qemu-devel@nongnu.org; Tue, 18 Dec 2018 06:22:34 -0500 Received: from mail.ispras.ru ([83.149.199.45]:55738) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1gZDSK-0006T8-HB for qemu-devel@nongnu.org; Tue, 18 Dec 2018 06:22:32 -0500 Received: from [127.0.1.1] (unknown [85.142.117.226]) by mail.ispras.ru (Postfix) with ESMTPSA id 67AAC54006A; Tue, 18 Dec 2018 14:22:31 +0300 (MSK) From: Pavel Dovgalyuk To: qemu-devel@nongnu.org Date: Tue, 18 Dec 2018 14:22:33 +0300 Message-ID: <20181218112233.11727.40569.stgit@pasha-VirtualBox> In-Reply-To: <20181218112056.11727.96529.stgit@pasha-VirtualBox> References: <20181218112056.11727.96529.stgit@pasha-VirtualBox> User-Agent: StGit/0.17.1-dirty MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable X-detected-operating-system: by eggs.gnu.org: GNU/Linux 3.x [fuzzy] X-Received-From: 83.149.199.45 Subject: [Qemu-devel] [PATCH v8 17/20] replay: describe reverse debugging in docs/replay.txt X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: kwolf@redhat.com, peter.maydell@linaro.org, war2jordan@live.com, pavel.dovgaluk@ispras.ru, pbonzini@redhat.com, crosthwaite.peter@gmail.com, ciro.santilli@gmail.com, jasowang@redhat.com, quintela@redhat.com, armbru@redhat.com, mreitz@redhat.com, alex.bennee@linaro.org, maria.klimushenkova@ispras.ru, mst@redhat.com, kraxel@redhat.com, boost.lists@gmail.com, thomas.dullien@googlemail.com, dovgaluk@ispras.ru, artem.k.pisarenko@gmail.com, dgilbert@redhat.com, rth@twiddle.net Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: "Qemu-devel" This patch updates the documentation and describes usage of the reverse debugging in QEMU+GDB. Signed-off-by: Pavel Dovgalyuk --- docs/replay.txt | 33 +++++++++++++++++++++++++++++++++ 1 file changed, 33 insertions(+) diff --git a/docs/replay.txt b/docs/replay.txt index 2c2c5f6..8447fdd 100644 --- a/docs/replay.txt +++ b/docs/replay.txt @@ -293,6 +293,39 @@ for recording and replaying must contain identical num= ber of ports in record and replay modes, but their backends may differ. E.g., '-serial stdio' in record mode, and '-serial null' in replay mode. =20 +Reverse debugging +----------------- + +Reverse debugging allows "executing" the program in reverse direction. +GDB remote protocol supports "reverse step" and "reverse continue" +commands. The first one steps single instruction backwards in time, +and the second one finds the last breakpoint in the past. + +Recorded executions may be used to enable reverse debugging. QEMU can't +execute the code in backwards direction, but can load a snapshot and +replay forward to find the desired position or breakpoint. + +The following GDB commands are supported: + - reverse-stepi (or rsi) - step one instruction backwards + - reverse-continue (or rc) - find last breakpoint in the past + +Reverse step loads the nearest snapshot and replays the execution until +the required instruction is met. + +Reverse continue may include several passes of examining the execution +between the snapshots. Each of the passes include the following steps: + 1. loading the snapshot + 2. replaying to examine the breakpoints + 3. if breakpoint or watchpoint was met + - loading the snaphot again + - replaying to the required breakpoint + 4. else + - proceeding to the p.1 with the earlier snapshot + +Therefore usage of the reverse debugging requires at least one snapshot +created in advance. See the "Snapshotting" section to learn about running +record/replay and creating the snapshot in these modes. + Replay log format ----------------- =20