From nobody Sat Sep 27 11:46:56 2025 Delivered-To: importer@patchew.org Received-SPF: pass (zoho.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; 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 209.51.188.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org Return-Path: Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) by mx.zohomail.com with SMTPS id 1547036808619376.50148095478505; Wed, 9 Jan 2019 04:26:48 -0800 (PST) Received: from localhost ([127.0.0.1]:49657 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ghCwU-00064O-O4 for importer@patchew.org; Wed, 09 Jan 2019 07:26:42 -0500 Received: from eggs.gnu.org ([209.51.188.92]:33612) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ghCjM-0004Fu-1S for qemu-devel@nongnu.org; Wed, 09 Jan 2019 07:13:08 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ghCjK-00025q-Ur for qemu-devel@nongnu.org; Wed, 09 Jan 2019 07:13:07 -0500 Received: from mail.ispras.ru ([83.149.199.45]:37394) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ghCjJ-00024m-SU for qemu-devel@nongnu.org; Wed, 09 Jan 2019 07:13:06 -0500 Received: from [127.0.1.1] (unknown [85.142.117.226]) by mail.ispras.ru (Postfix) with ESMTPSA id 6BD9554006B; Wed, 9 Jan 2019 15:13:04 +0300 (MSK) From: Pavel Dovgalyuk To: qemu-devel@nongnu.org Date: Wed, 09 Jan 2019 15:13:04 +0300 Message-ID: <154703598429.13472.18387436180159033352.stgit@pasha-VirtualBox> In-Reply-To: <154703587757.13472.3898702635363120794.stgit@pasha-VirtualBox> References: <154703587757.13472.3898702635363120794.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 X-Received-From: 83.149.199.45 Subject: [Qemu-devel] [PATCH v9 18/21] 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