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 <Pavel.Dovgalyuk@ispras.ru>

--

v6:
 - dropped unused error processing (suggested by Philippe Mathieu-Daudé)
Message-Id: <160174524096.12451.11651270339216758643.stgit@pasha-ThinkPad-X280>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 14 insertions, 0 deletions

diff --git a/replay/replay-debugging.c b/replay/replay-debugging.c
index 30ca38e..ee9e86d 100644
--- 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. */
+        }
+    }
+}