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

[Pedro Alves <palves@redhat.com>]

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.

This needs a NEWS and docs review.

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".
---
 gdb/doc/gdb.texinfo |    4 ++++
 1 file changed, 4 insertions(+)

diff --git a/gdb/NEWS b/gdb/NEWS
index 77a27f7..56b68d8 100644
--- a/gdb/NEWS
+++ b/gdb/NEWS
@@ -10,6 +10,12 @@ maint set|show per-command time
 maint set|show per-command symtab
   Enable display of per-command gdb resource usage.
 
+* New options
+
+set remote trace-status-packet
+show remote trace-status-packet
+  Set/show the use of remote protocol qTStatus packet.
+
 * The command 'tsave' can now support new option '-ctf' to save trace
   buffer in Common Trace Format.
 
diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index 38ce259..05ac6c0 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -18446,6 +18446,10 @@ are:
 @tab @code{qAttached}
 @tab Querying remote process attach state.
 
+@item @code{trace-status}
+@tab @code{qTStatus}
+@tab @code{tstatus}
+
 @item @code{traceframe-info}
 @tab @code{qXfer:traceframe-info:read}
 @tab Traceframe info
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);