@@ -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
-----------------
This patch updates the documentation and describes usage of the reverse debugging in QEMU+GDB. Signed-off-by: Pavel Dovgalyuk <Pavel.Dovgaluk@ispras.ru> --- docs/replay.txt | 33 +++++++++++++++++++++++++++++++++ 1 file changed, 33 insertions(+)