gdbstub: add reverse continue support in replay mode

This patch adds support of the reverse continue operation for gdbstub.
Reverse continue finds the last breakpoint that would happen in normal
execution from the beginning to the current moment.
Implementation of the reverse continue replays the execution twice:
to find the breakpoints that were hit and to seek to the last breakpoint.
Reverse continue loads the previous snapshot and tries to find the breakpoint
since that moment. If there are no such breakpoints, it proceeds to
the earlier snapshot, and so on. When no breakpoints or watchpoints were
hit at all, execution stops at the beginning of the replay log.

Signed-off-by: Pavel Dovgalyuk <Pavel.Dovgalyuk@ispras.ru>
Message-Id: <160174522930.12451.6994758004725016836.stgit@pasha-ThinkPad-X280>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 9 insertions, 1 deletions

diff --git a/gdbstub.c b/gdbstub.c
index 79e8ccc050..ac92273018 100644
--- a/gdbstub.c
+++ b/gdbstub.c
@@ -1907,6 +1907,13 @@ static void handle_backward(GdbCmdContext *gdb_ctx, void *user_ctx)
                 put_packet("E14");
             }
             return;
+        case 'c':
+            if (replay_reverse_continue()) {
+                gdb_continue();
+            } else {
+                put_packet("E14");
+            }
+            return;
         }
     }
 
@@ -2161,7 +2168,8 @@ static void handle_query_supported(GdbCmdContext *gdb_ctx, void *user_ctx)
     }
 
     if (replay_mode == REPLAY_MODE_PLAY) {
-        g_string_append(gdbserver_state.str_buf, ";ReverseStep+");
+        g_string_append(gdbserver_state.str_buf,
+            ";ReverseStep+;ReverseContinue+");
     }
 
     if (gdb_ctx->num_params &&