[11/13] gdbstub: add reverse continue support in replay mode

diff --git a/cpus.c b/cpus.c
index 35381ea941..6aed096eab 100644
--- a/cpus.c
+++ b/cpus.c
@@ -1106,6 +1106,11 @@  static void cpu_handle_guest_debug(CPUState *cpu)
         cpu->stopped = true;
     } else {
         if (!cpu->singlestep_enabled) {
+            /*
+             * Report about the breakpoint and
+             * make a single step to skip it
+             */
+            replay_breakpoint();
             cpu_single_step(cpu, SSTEP_ENABLE);
         } else {
             cpu_single_step(cpu, 0);
diff --git a/exec.c b/exec.c
index 4bde79ea3b..0f4665d858 100644
--- a/exec.c
+++ b/exec.c
@@ -2725,6 +2725,7 @@  void cpu_check_watchpoint(CPUState *cpu, vaddr addr, vaddr len,
                  * Don't process the watchpoints when we are
                  * in a reverse debugging operation.
                  */
+                replay_breakpoint();
                 return;
             }
             if (flags == BP_MEM_READ) {
diff --git a/gdbstub.c b/gdbstub.c
index a81b3b5fb8..5d1cb2dde1 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 &&
diff --git a/include/sysemu/replay.h b/include/sysemu/replay.h
index 13a8123b09..b6cac175c4 100644
--- a/include/sysemu/replay.h
+++ b/include/sysemu/replay.h
@@ -81,11 +81,19 @@  const char *replay_get_filename(void);
  * Returns true on success.
  */
 bool replay_reverse_step(void);
+/*
+ * Start searching the last breakpoint/watchpoint.
+ * Used by gdbstub for backwards debugging.
+ * Returns true if the process successfully started.
+ */
+bool replay_reverse_continue(void);
 /*
  * Returns true if replay module is processing
  * reverse_continue or reverse_step request
  */
 bool replay_running_debug(void);
+/* Called in reverse debugging mode to collect breakpoint information */
+void replay_breakpoint(void);
 
 /* Processing the instructions */
 
diff --git a/replay/replay-debugging.c b/replay/replay-debugging.c
index aa3ca040e2..27af103118 100644
--- a/replay/replay-debugging.c
+++ b/replay/replay-debugging.c
@@ -23,6 +23,8 @@ 
 #include "migration/snapshot.h"
 
 static bool replay_is_debugging;
+static int64_t replay_last_breakpoint;
+static int64_t replay_last_snapshot;
 
 bool replay_running_debug(void)
 {
@@ -252,3 +254,72 @@  bool replay_reverse_step(void)
 
     return false;
 }
+
+static void replay_continue_end(void)
+{
+    replay_is_debugging = false;
+    vm_stop(RUN_STATE_DEBUG);
+    replay_delete_break();
+}
+
+static void replay_continue_stop(void *opaque)
+{
+    Error *err = NULL;
+    if (replay_last_breakpoint != -1LL) {
+        replay_seek(replay_last_breakpoint, replay_stop_vm_debug, &err);
+        if (err) {
+            error_free(err);
+            replay_continue_end();
+        }
+        return;
+    }
+    /*
+     * No breakpoints since the last snapshot.
+     * Find previous snapshot and try again.
+     */
+    if (replay_last_snapshot != 0) {
+        replay_seek(replay_last_snapshot - 1, replay_continue_stop, &err);
+        if (err) {
+            error_free(err);
+            replay_continue_end();
+        }
+        replay_last_snapshot = replay_get_current_icount();
+        return;
+    } else {
+        /* Seek to the very first step */
+        replay_seek(0, replay_stop_vm_debug, &err);
+        if (err) {
+            error_free(err);
+            replay_continue_end();
+        }
+        return;
+    }
+    replay_continue_end();
+}
+
+bool replay_reverse_continue(void)
+{
+    Error *err = NULL;
+
+    assert(replay_mode == REPLAY_MODE_PLAY);
+
+    if (replay_get_current_icount() != 0) {
+        replay_seek(replay_get_current_icount() - 1, replay_continue_stop, &err);
+        if (err) {
+            error_free(err);
+            return false;
+        }
+        replay_last_breakpoint = -1LL;
+        replay_is_debugging = true;
+        replay_last_snapshot = replay_get_current_icount();
+        return true;
+    }
+
+    return false;
+}
+
+void replay_breakpoint(void)
+{
+    assert(replay_mode == REPLAY_MODE_PLAY);
+    replay_last_breakpoint = replay_get_current_icount();
+}
diff --git a/stubs/replay.c b/stubs/replay.c
index d5b52302e9..45ebe77fb9 100644
--- a/stubs/replay.c
+++ b/stubs/replay.c
@@ -98,3 +98,8 @@  bool replay_reverse_step(void)
 {
     return false;
 }
+
+bool replay_reverse_continue(void)
+{
+    return false;
+}