Stop sending qTStatus if the target doesn't recognize it; add packet configuration command.

GDB currently sends a qTStatus even if the target previously replied
an empty packet to a previous qTStatus.  If the target doesn't
recognize the packet, there's no point in trying again.

The machinery we have in place is packet_ok, which has the nice side
effect of forcing one to install a configuration command/knob for the
packet in question, which is often handy when you need to debug
things, and/or emulate a target that doesn't support the packet, or even,
it can be used as workaround for the old broken kgdb's that return error
to qTSTatus instead of an empty packet.

gdb/
2013-03-28  Pedro Alves  <palves@redhat.com>

	* NEWS (New options): New section.
	(New options): Mention set/show remote trace-status-packet.
	* remote.c (PACKET_qTStatus): New enumeration value.
	(remote_get_trace_status): Skip sending qTStatus if the packet is
	disabled.  Use packet_ok.
	(_initialize_remote): Register a configuration command for
	qTStatus packet.

gdb/doc/
2013-03-28  Pedro Alves  <palves@redhat.com>

	* gdb.texinfo (Remote Configuration) <set remote @var{name}-packet
	table>: Add entry for "trace-status".

1 files changed, 11 insertions, 1 deletions

diff --git a/gdb/remote.c b/gdb/remote.c
index 8659953..b8a7a1a 100644
--- a/gdb/remote.c
+++ b/gdb/remote.c
@@ -1256,6 +1256,7 @@ enum {
   PACKET_qGetTIBAddr,
   PACKET_qGetTLSAddr,
   PACKET_qSupported,
+  PACKET_qTStatus,
   PACKET_QPassSignals,
   PACKET_QProgramSignals,
   PACKET_qSearch_memory,
@@ -10689,6 +10690,10 @@ remote_get_trace_status (struct trace_status *ts)
   /* FIXME we need to get register block size some other way.  */
   extern int trace_regblock_size;
   volatile struct gdb_exception ex;
+  enum packet_result result;
+
+  if (remote_protocol_packets[PACKET_qTStatus].support == PACKET_DISABLE)
+    return -1;
 
   trace_regblock_size = get_remote_arch_state ()->sizeof_g_packet;
 
@@ -10707,8 +10712,10 @@ remote_get_trace_status (struct trace_status *ts)
       throw_exception (ex);
     }
 
+  result = packet_ok (p, &remote_protocol_packets[PACKET_qTStatus]);
+
   /* If the remote target doesn't do tracing, flag it.  */
-  if (*p == '\0')
+  if (result == PACKET_UNKNOWN)
     return -1;
 
   /* We're working with a live target.  */
@@ -11876,6 +11883,9 @@ Show the maximum size of the address (in bits) in a memory packet."), NULL,
   add_packet_config_cmd (&remote_protocol_packets[PACKET_qSearch_memory],
 			 "qSearch:memory", "search-memory", 0);
 
+  add_packet_config_cmd (&remote_protocol_packets[PACKET_qTStatus],
+			 "qTStatus", "trace-status", 0);
+
   add_packet_config_cmd (&remote_protocol_packets[PACKET_vFile_open],
 			 "vFile:open", "hostio-open", 0);