replay: create temporary snapshot at debugger connection

When record/replay does not uses overlays for storing the snapshots, user is not capable of issuing reverse debugging commands. This patch adds creation of the VM snapshot on the temporary overlay image, when the debugger connects to QEMU. Therefore the execution can be rewind to the moment of the debugger connection while debugging the virtual machine. Signed-off-by: Pavel Dovgalyuk <[email protected]> -- v6: - dropped unused error processing (suggested by Philippe Mathieu-Daudé) Message-Id: <160174524096.12451.11651270339216758643.stgit@pasha-ThinkPad-X280> Signed-off-by: Paolo Bonzini <[email protected]>
httoracle · Oct 6, 2020 · 56357d8 · 56357d8
1 parent 9a608af
commit 56357d8
Show file tree

Hide file tree

Showing 3 changed files with 17 additions and 0 deletions.
diff --git a/gdbstub.c b/gdbstub.c
@@ -3321,6 +3321,7 @@ static void gdb_chr_event(void *opaque, QEMUChrEvent event)
         s->g_cpu = s->c_cpu;
 
         vm_stop(RUN_STATE_PAUSED);
+        replay_gdb_attached();
         gdb_has_xml = false;
         break;
     default:

diff --git a/include/sysemu/replay.h b/include/sysemu/replay.h
@@ -94,6 +94,8 @@ bool replay_reverse_continue(void);
 bool replay_running_debug(void);
 /* Called in reverse debugging mode to collect breakpoint information */
 void replay_breakpoint(void);
+/* Called when gdb is attached to gdbstub */
+void replay_gdb_attached(void);
 
 /* Processing the instructions */
 

diff --git a/replay/replay-debugging.c b/replay/replay-debugging.c
@@ -318,3 +318,17 @@ void replay_breakpoint(void)
     assert(replay_mode == REPLAY_MODE_PLAY);
     replay_last_breakpoint = replay_get_current_icount();
 }
+
+void replay_gdb_attached(void)
+{
+    /*
+     * Create VM snapshot on temporary overlay to allow reverse
+     * debugging even if snapshots were not enabled.
+     */
+    if (replay_mode == REPLAY_MODE_PLAY
+        && !replay_snapshot) {
+        if (save_snapshot("start_debugging", NULL) != 0) {
+            /* Can't create the snapshot. Continue conventional debugging. */
+        }
+    }
+}