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[PATCH 12/13] replay: describe reverse debugging in docs/replay.txt
From: |
Pavel Dovgalyuk |
Subject: |
[PATCH 12/13] replay: describe reverse debugging in docs/replay.txt |
Date: |
Fri, 26 Jun 2020 13:20:48 +0300 |
User-agent: |
StGit/0.17.1-dirty |
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
-----------------
- [PATCH 00/13] Reverse debugging, Pavel Dovgalyuk, 2020/06/26
- [PATCH 08/13] replay: implement replay-seek command, Pavel Dovgalyuk, 2020/06/26
- [PATCH 10/13] gdbstub: add reverse step support in replay mode, Pavel Dovgalyuk, 2020/06/26
- [PATCH 06/13] replay: introduce info hmp/qmp command, Pavel Dovgalyuk, 2020/06/26
- [PATCH 03/13] migration: introduce icount field for snapshots, Pavel Dovgalyuk, 2020/06/26
- [PATCH 09/13] replay: flush rr queue before loading the vmstate, Pavel Dovgalyuk, 2020/06/26
- [PATCH 12/13] replay: describe reverse debugging in docs/replay.txt,
Pavel Dovgalyuk <=
- [PATCH 13/13] tests/acceptance: add reverse debugging test, Pavel Dovgalyuk, 2020/06/26
- [PATCH 01/13] replay: provide an accessor for rr filename, Pavel Dovgalyuk, 2020/06/26
- [PATCH 02/13] qcow2: introduce icount field for snapshots, Pavel Dovgalyuk, 2020/06/26
- [PATCH 04/13] iotests: update snapshot test for new output format, Pavel Dovgalyuk, 2020/06/26
- [PATCH 05/13] qapi: introduce replay.json for record/replay-related stuff, Pavel Dovgalyuk, 2020/06/26
- [PATCH 07/13] replay: introduce breakpoint at the specified step, Pavel Dovgalyuk, 2020/06/26
- [PATCH 11/13] gdbstub: add reverse continue support in replay mode, Pavel Dovgalyuk, 2020/06/26