From nobody Sat Oct 25 17:18:43 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; dmarc=fail(p=none dis=none) header.from=gmail.com ARC-Seal: i=1; a=rsa-sha256; t=1561106787; cv=none; d=zoho.com; s=zohoarc; b=P2LVjEatAy/JnnV65Tuo2SGIOS92GsVLZo9kwCSLRpUQenjsMWNyfRHaPSrtC5JVHQx/2LLsmGFrsI4tidNmB1oNanfj7eGQp7wy68gOu2KkNbVvUZKXReNyjeaC6XEoUmtp3VpTcpTfYJ7TUv6Ep3MYmgW+MWrrgpZascz7M6s= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=zoho.com; s=zohoarc; t=1561106787; h=Content-Type:Content-Transfer-Encoding:Cc:Date:From:In-Reply-To:List-Subscribe:List-Post:List-Id:List-Archive:List-Help:List-Unsubscribe:MIME-Version:Message-ID:References:Sender:Subject:To:ARC-Authentication-Results; bh=jkRxllQQz0yK9Kr7lOv/tAFNECQjPLkj3d4iZYgQRnA=; b=W5MaZ8g1yI5jeQiuVl6AJoBvkQheRcSAP6BE9U1jOenYD0gYARZChmbKj2k18lrVCeVkh7RMx7KD4IaOnS023bRJFIXJ2kCvRrBqRhLcBR+hy7j+XWcTTzIu0oiFJmBS/JaprnoP2616sd61jFSEeTJmZI0U5PAmR1FEMFrPI+A= ARC-Authentication-Results: i=1; mx.zoho.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; dmarc=fail header.from= (p=none dis=none) header.from= Return-Path: Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) by mx.zohomail.com with SMTPS id 1561106787757377.63346329255785; Fri, 21 Jun 2019 01:46:27 -0700 (PDT) Received: from localhost ([::1]:55564 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1heFBg-0003lp-5S for importer@patchew.org; Fri, 21 Jun 2019 04:46:24 -0400 Received: from eggs.gnu.org ([209.51.188.92]:58236) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1heEza-0004B8-5M for qemu-devel@nongnu.org; Fri, 21 Jun 2019 04:33:56 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1heEoP-0001FQ-CI for qemu-devel@nongnu.org; Fri, 21 Jun 2019 04:22:22 -0400 Received: from mail.ispras.ru ([83.149.199.45]:41636) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1heEoP-0001EU-5v for qemu-devel@nongnu.org; Fri, 21 Jun 2019 04:22:21 -0400 Received: from [127.0.1.1] (unknown [85.142.117.226]) by mail.ispras.ru (Postfix) with ESMTPSA id 4BBC7540082; Fri, 21 Jun 2019 11:22:20 +0300 (MSK) From: Pavel Dovgalyuk To: qemu-devel@nongnu.org Date: Fri, 21 Jun 2019 11:22:20 +0300 Message-ID: <156110534010.25431.470716625287653564.stgit@pasha-Precision-3630-Tower> In-Reply-To: <156110523748.25431.9310430853468653085.stgit@pasha-Precision-3630-Tower> References: <156110523748.25431.9310430853468653085.stgit@pasha-Precision-3630-Tower> 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 for-4.1 18/24] replay: describe reverse debugging in docs/replay.txt X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: kwolf@redhat.com, peter.maydell@linaro.org, pavel.dovgaluk@ispras.ru, pbonzini@redhat.com, quintela@redhat.com, ciro.santilli@gmail.com, jasowang@redhat.com, crosthwaite.peter@gmail.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" From: Pavel Dovgalyuk 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 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