From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:39599) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1fiIiY-00036e-M2 for qemu-devel@nongnu.org; Wed, 25 Jul 2018 08:16:38 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1fiIiV-0006KD-Lf for qemu-devel@nongnu.org; Wed, 25 Jul 2018 08:16:34 -0400 Received: from mail.ispras.ru ([83.149.199.45]:36828) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1fiIiV-0006JE-Bg for qemu-devel@nongnu.org; Wed, 25 Jul 2018 08:16:31 -0400 From: Pavel Dovgalyuk Date: Wed, 25 Jul 2018 15:16:32 +0300 Message-ID: <20180725121632.12867.76576.stgit@pasha-VirtualBox> In-Reply-To: <20180725121311.12867.21729.stgit@pasha-VirtualBox> References: <20180725121311.12867.21729.stgit@pasha-VirtualBox> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Subject: [Qemu-devel] [PATCH v5 18/24] replay: describe reverse debugging in docs/replay.txt List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: kwolf@redhat.com, peter.maydell@linaro.org, war2jordan@live.com, crosthwaite.peter@gmail.com, boost.lists@gmail.com, quintela@redhat.com, ciro.santilli@gmail.com, jasowang@redhat.com, mst@redhat.com, zuban32s@gmail.com, armbru@redhat.com, maria.klimushenkova@ispras.ru, dovgaluk@ispras.ru, kraxel@redhat.com, pavel.dovgaluk@ispras.ru, thomas.dullien@googlemail.com, pbonzini@redhat.com, mreitz@redhat.com, alex.bennee@linaro.org, dgilbert@redhat.com, rth@twiddle.net 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 f7def53..086d3f8 100644 --- a/docs/replay.txt +++ b/docs/replay.txt @@ -293,6 +293,39 @@ for recording and replaying must contain identical number 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. +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 -----------------