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From: Pavel Dovgalyuk <pavel.dovgalyuk@ispras.ru>
To: qemu-devel@nongnu.org
Cc: kwolf@redhat.com, wrampazz@redhat.com, pavel.dovgalyuk@ispras.ru,
	ehabkost@redhat.com, alex.bennee@linaro.org, mtosatti@redhat.com,
	armbru@redhat.com, mreitz@redhat.com, stefanha@redhat.com,
	crosa@redhat.com, pbonzini@redhat.com, philmd@redhat.com,
	zhiwei_liu@c-sky.com, rth@twiddle.net
Subject: [PATCH 12/13] replay: describe reverse debugging in docs/replay.txt
Date: Fri, 26 Jun 2020 13:20:48 +0300	[thread overview]
Message-ID: <159316684833.10508.798035270216502557.stgit@pasha-ThinkPad-X280> (raw)
In-Reply-To: <159316678008.10508.6615172353109944370.stgit@pasha-ThinkPad-X280>

From: Pavel Dovgalyuk <Pavel.Dovgaluk@ispras.ru>

This patch updates the documentation and describes usage of the reverse
debugging in QEMU+GDB.

Signed-off-by: Pavel Dovgalyuk <Pavel.Dovgalyuk@ispras.ru>
---
 0 files changed

diff --git a/docs/replay.txt b/docs/replay.txt
index 70c27edb36..18d6169f3b 100644
--- a/docs/replay.txt
+++ b/docs/replay.txt
@@ -294,6 +294,39 @@ 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
 -----------------
 



  parent reply	other threads:[~2020-06-26 13:42 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-26 10:19 [PATCH 00/13] Reverse debugging Pavel Dovgalyuk
2020-06-26 10:19 ` [PATCH 01/13] replay: provide an accessor for rr filename Pavel Dovgalyuk
2020-06-26 10:19 ` [PATCH 02/13] qcow2: introduce icount field for snapshots Pavel Dovgalyuk
2020-07-06 20:17   ` Eric Blake
2020-07-16  6:43     ` Pavel Dovgalyuk
2020-06-26 10:19 ` [PATCH 03/13] migration: " Pavel Dovgalyuk
2020-06-26 10:20 ` [PATCH 04/13] iotests: update snapshot test for new output format Pavel Dovgalyuk
2020-06-26 10:20 ` [PATCH 05/13] qapi: introduce replay.json for record/replay-related stuff Pavel Dovgalyuk
2020-07-15 11:20   ` Alex Bennée
2020-07-16  6:00     ` Pavel Dovgalyuk
2020-06-26 10:20 ` [PATCH 06/13] replay: introduce info hmp/qmp command Pavel Dovgalyuk
2020-06-26 10:20 ` [PATCH 07/13] replay: introduce breakpoint at the specified step Pavel Dovgalyuk
2020-06-26 10:20 ` [PATCH 08/13] replay: implement replay-seek command Pavel Dovgalyuk
2020-06-26 10:20 ` [PATCH 09/13] replay: flush rr queue before loading the vmstate Pavel Dovgalyuk
2020-06-26 10:20 ` [PATCH 10/13] gdbstub: add reverse step support in replay mode Pavel Dovgalyuk
2020-07-15 11:27   ` Alex Bennée
2020-06-26 10:20 ` [PATCH 11/13] gdbstub: add reverse continue " Pavel Dovgalyuk
2020-06-26 10:20 ` Pavel Dovgalyuk [this message]
2020-06-26 10:20 ` [PATCH 13/13] tests/acceptance: add reverse debugging test Pavel Dovgalyuk
2020-07-06  6:02 ` [PATCH 00/13] Reverse debugging Pavel Dovgalyuk
2020-07-06 19:55   ` Alex Bennée
2020-07-07  5:00     ` Pavel Dovgalyuk

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