From patchwork Fri Mar 15 12:10:01 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Pavel Dovgalyuk X-Patchwork-Id: 10854733 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 0BFC61575 for ; Fri, 15 Mar 2019 13:29:45 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id E35162A970 for ; Fri, 15 Mar 2019 13:29:44 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id D64142A9B5; Fri, 15 Mar 2019 13:29:44 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.9 required=2.0 tests=BAYES_00,MAILING_LIST_MULTI autolearn=ham version=3.3.1 Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (No client certificate requested) by mail.wl.linuxfoundation.org (Postfix) with ESMTPS id 7FE382A9B9 for ; Fri, 15 Mar 2019 13:29:44 +0000 (UTC) Received: from localhost ([127.0.0.1]:55050 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1h4mu7-0000Qr-RR for patchwork-qemu-devel@patchwork.kernel.org; Fri, 15 Mar 2019 09:29:43 -0400 Received: from eggs.gnu.org ([209.51.188.92]:51462) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1h4mU6-0003Hu-0m for qemu-devel@nongnu.org; Fri, 15 Mar 2019 09:02:51 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1h4mDS-0007WP-V1 for qemu-devel@nongnu.org; Fri, 15 Mar 2019 08:45:40 -0400 Received: from mail.ispras.ru ([83.149.199.45]:39813) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1h4mDR-0007SA-5P for qemu-devel@nongnu.org; Fri, 15 Mar 2019 08:45:38 -0400 Received: from [127.0.1.1] (unknown [85.142.117.226]) by mail.ispras.ru (Postfix) with ESMTPSA id B50B8540143; Fri, 15 Mar 2019 15:10:07 +0300 (MSK) From: Pavel Dovgalyuk To: qemu-devel@nongnu.org Date: Fri, 15 Mar 2019 15:10:01 +0300 Message-ID: <155265180132.20013.9680133378007850167.stgit@pasha-VirtualBox> In-Reply-To: <155265169782.20013.5884232667053404718.stgit@pasha-VirtualBox> References: <155265169782.20013.5884232667053404718.stgit@pasha-VirtualBox> User-Agent: StGit/0.17.1-dirty MIME-Version: 1.0 X-detected-operating-system: by eggs.gnu.org: GNU/Linux 3.x X-Received-From: 83.149.199.45 Subject: [Qemu-devel] [PATCH v14 18/25] 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+patchwork-qemu-devel=patchwork.kernel.org@nongnu.org Sender: "Qemu-devel" X-Virus-Scanned: ClamAV using ClamSMTP 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 ce97c3f72f..47b4f2d9f8 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 -----------------