Add support for the '!' extended mode packet. This is required for the
multiprocess extension.

Signed-off-by: Luc Michel <luc.michel@greensocs.com>
---
 gdbstub.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/gdbstub.c b/gdbstub.c
index af8864e251..4bed0a85f3 100644
--- a/gdbstub.c
+++ b/gdbstub.c
@@ -1281,10 +1281,13 @@ static int gdb_handle_packet(GDBState *s, const char *line_buf)
     trace_gdbstub_io_command(line_buf);
 
     p = line_buf;
     ch = *p++;
     switch(ch) {
+    case '!':
+        put_packet(s, "OK");
+        break;
     case '?':
         /* TODO: Make this return the correct value for user-mode.  */
         snprintf(buf, sizeof(buf), "T%02xthread:%s;", GDB_SIGNAL_TRAP,
                  get_thread_id(s, s->c_cpu, thread_id, sizeof(thread_id)));
         put_packet(s, buf);
-- 
2.18.0