[RFC][patch] Allow user to disable tracepoint support in gdbserver via command line

[ppluzhnikov at google dot com (Paul Pluzhnikov)]

Greetings,

Following up on my earlier "slow on high-latency links" message:
http://sourceware.org/ml/gdb-patches/2011-07/msg00391.html ...

Another source of major slowness for me is the gdbserver querying for
tracepoint symbols.

I see repeated (for each SOLIB) sequences of:

00:00:44 Sending packet: $qSymbol::#5b...Packet received: qSymbol:6764625f6167656e745f6764625f74705f686561705f627566666572
00:00:44 Packet qSymbol (symbol-lookup) is supported
00:00:44 Sending packet: $qSymbol::6764625f6167656e745f6764625f74705f686561705f627566666572#1e...Packet received: qSymbol:6764625f6167656e745f6764625f6a756d705f7061645f627566666572
00:00:44 Sending packet: $qSymbol::6764625f6167656e745f6764625f6a756d705f7061645f627566666572#e1...Packet received: qSymbol:6764625f6167656e745f6764625f6a756d705f7061645f6275666665725f656e64
00:00:44 Sending packet: $qSymbol::6764625f6167656e745f6764625f6a756d705f7061645f6275666665725f656e64#ec...Packet received: qSymbol:6764625f6167656e745f636f6c6c656374696e67
00:00:44 Sending packet: $qSymbol::6764625f6167656e745f636f6c6c656374696e67#02...Packet received: qSymbol:6764625f6167656e745f6764625f636f6c6c656374
00:00:45 Sending packet: $qSymbol::6764625f6167656e745f6764625f636f6c6c656374#65...Packet received: qSymbol:6764625f6167656e745f73746f705f74726163696e67
00:00:45 Sending packet: $qSymbol::6764625f6167656e745f73746f705f74726163696e67#a3...Packet received: qSymbol:6764625f6167656e745f666c7573685f74726163655f627566666572
00:00:45 Sending packet: $qSymbol::6764625f6167656e745f666c7573685f74726163655f627566666572#23...Packet received: qSymbol:6764625f6167656e745f61626f75745f746f5f726571756573745f6275666665725f7370616365
00:00:45 Sending packet: $qSymbol::6764625f6167656e745f61626f75745f746f5f726571756573745f6275666665725f7370616365#3e...Packet received: qSymbol:6764625f6167656e745f74726163655f6275666665725f69735f66756c6c
00:00:45 Sending packet: $qSymbol::6764625f6167656e745f74726163655f6275666665725f69735f66756c6c#58...Packet received: qSymbol:6764625f6167656e745f73746f7070696e675f7472616365706f696e74
00:00:45 Sending packet: $qSymbol::6764625f6167656e745f73746f7070696e675f7472616365706f696e74#ed...Packet received: qSymbol:6764625f6167656e745f657870725f6576616c5f726573756c74
00:00:46 Sending packet: $qSymbol::6764625f6167656e745f657870725f6576616c5f726573756c74#7b...Packet received: qSymbol:6764625f6167656e745f6572726f725f7472616365706f696e74
00:00:46 Sending packet: $qSymbol::6764625f6167656e745f6572726f725f7472616365706f696e74#79...Packet received: qSymbol:6764625f6167656e745f7472616365706f696e7473
00:00:46 Sending packet: $qSymbol::6764625f6167656e745f7472616365706f696e7473#06...Packet received: qSymbol:6764625f6167656e745f74726163696e67
00:00:46 Sending packet: $qSymbol::6764625f6167656e745f74726163696e67#30...Packet received: qSymbol:6764625f6167656e745f74726163655f6275666665725f6374726c
00:00:46 Sending packet: $qSymbol::6764625f6167656e745f74726163655f6275666665725f6374726c#b0...Packet received: qSymbol:6764625f6167656e745f74726163655f6275666665725f6374726c5f63757272
00:00:46 Sending packet: $qSymbol::6764625f6167656e745f74726163655f6275666665725f6374726c5f63757272#f2...Packet received: qSymbol:6764625f6167656e745f74726163655f6275666665725f6c6f
00:00:47 Sending packet: $qSymbol::6764625f6167656e745f74726163655f6275666665725f6c6f#0f...Packet received: qSymbol:6764625f6167656e745f74726163655f6275666665725f6869
00:00:47 Sending packet: $qSymbol::6764625f6167656e745f74726163655f6275666665725f6869#b7...Packet received: qSymbol:6764625f6167656e745f74726163656672616d655f726561645f636f756e74
00:00:47 Sending packet: $qSymbol::6764625f6167656e745f74726163656672616d655f726561645f636f756e74#b7...Packet received: qSymbol:6764625f6167656e745f74726163656672616d655f77726974655f636f756e74
00:00:47 Sending packet: $qSymbol::6764625f6167656e745f74726163656672616d655f77726974655f636f756e74#2e...Packet received: qSymbol:6764625f6167656e745f74726163656672616d65735f63726561746564
00:00:47 Sending packet: $qSymbol::6764625f6167656e745f74726163656672616d65735f63726561746564#4e...Packet received: qSymbol:6764625f6167656e745f74726163655f73746174655f7661726961626c6573
00:00:47 Sending packet: $qSymbol::6764625f6167656e745f74726163655f73746174655f7661726961626c6573#55...Packet received: qSymbol:6764625f6167656e745f6765745f7261775f726567
00:00:48 Sending packet: $qSymbol::6764625f6167656e745f6765745f7261775f726567#0d...Packet received: qSymbol:6764625f6167656e745f6765745f74726163655f73746174655f7661726961626c655f76616c7565
00:00:48 Sending packet: $qSymbol::6764625f6167656e745f6765745f74726163655f73746174655f7661726961626c655f76616c7565#a8...Packet received: qSymbol:6764625f6167656e745f7365745f74726163655f73746174655f7661726961626c655f76616c7565
00:00:48 Sending packet: $qSymbol::6764625f6167656e745f7365745f74726163655f73746174655f7661726961626c655f76616c7565#a5...Packet received: qSymbol:6764625f6167656e745f7573745f6c6f61646564
00:00:48 Sending packet: $qSymbol::6764625f6167656e745f7573745f6c6f61646564#cc...Packet received: qSymbol:6764625f6167656e745f68656c7065725f7468726561645f6964
00:00:48 Sending packet: $qSymbol::6764625f6167656e745f68656c7065725f7468726561645f6964#4f...Packet received: qSymbol:6764625f6167656e745f636d645f627566
00:00:48 Sending packet: $qSymbol::6764625f6167656e745f636d645f627566#5d...Packet received: qSymbol:6e70746c5f76657273696f6e
00:00:49 Sending packet: $qSymbol::6e70746c5f76657273696f6e#4d...Packet received: qSymbol:6e70746c5f76657273696f6e
00:00:49 Sending packet: $qSymbol::6e70746c5f76657273696f6e#4d...Packet received: qSymbol:6e70746c5f76657273696f6e
00:00:49 Sending packet: $qSymbol::6e70746c5f76657273696f6e#4d...Packet received: OK

Since I have 10 shared libraries in that executable, this costs me about
1 minute delay, and is completely wasted, because I am not going to use
tracepoints.

Attached patch allows me to disable tracepoint support via
--disable-tracepoints command line flag.

The patch would need documentation update, which I'll provide if the idea
of turning off tracepoints like that is not found too repulsive.

Thanks,
--
Paul Pluzhnikov


2011-07-19  Paul Pluzhnikov  <ppluzhnikov@google.com>

	* server.c (disable_tracepoints): New variable.
	(support_tracepoints_p): New function.
	(handle_general_set, handle_query): Use it.
	(main): Handle --disable-tracepoints.


Index: gdbserver/server.c
===================================================================
RCS file: /cvs/src/src/gdb/gdbserver/server.c,v
retrieving revision 1.145
diff -u -p -r1.145 server.c
--- gdbserver/server.c	12 May 2011 12:09:17 -0000	1.145
+++ gdbserver/server.c	15 Jul 2011 22:54:42 -0000
@@ -92,6 +92,9 @@ int disable_packet_Tthread;
 int disable_packet_qC;
 int disable_packet_qfThreadInfo;
 
+/* Set if you want to disable tracepoints.  */
+int disable_tracepoints;
+
 /* Last status reported to GDB.  */
 static struct target_waitstatus last_status;
 static ptid_t last_ptid;
@@ -117,6 +120,14 @@ struct vstop_notif
 /* The pending stop replies list head.  */
 static struct vstop_notif *notif_queue = NULL;
 
+/* Do we support tracepoints.  */
+
+static int
+support_tracepoints_p ()
+{
+  return !disable_tracepoints && target_supports_tracepoints ();
+}
+
 /* Put a stop reply to the stop reply queue.  */
 
 static void
@@ -498,8 +509,7 @@ handle_general_set (char *own_buf)
       return;
     }
 
-  if (target_supports_tracepoints ()
-      && handle_tracepoint_general_set (own_buf))
+  if (support_tracepoints_p () && handle_tracepoint_general_set (own_buf))
     return;
 
   /* Otherwise we didn't know what packet it was.  Say we didn't
@@ -1378,7 +1388,7 @@ handle_query (char *own_buf, int packet_
 	 we access breakpoint shadows.  */
       validate_breakpoints ();
 
-      if (target_supports_tracepoints ())
+      if (support_tracepoints_p ())
 	tracepoint_look_up_symbols ();
 
       if (target_running () && the_target->look_up_symbols != NULL)
@@ -1529,7 +1539,7 @@ handle_query (char *own_buf, int packet_
 
       strcat (own_buf, ";qXfer:threads:read+");
 
-      if (target_supports_tracepoints ())
+      if (support_tracepoints_p ())
 	{
 	  strcat (own_buf, ";ConditionalTracepoints+");
 	  strcat (own_buf, ";TraceStateVariables+");
@@ -1730,7 +1740,7 @@ handle_query (char *own_buf, int packet_
   if (handle_qxfer (own_buf, packet_len, new_packet_len_p))
     return;
 
-  if (target_supports_tracepoints () && handle_tracepoint_query (own_buf))
+  if (support_tracepoints_p () && handle_tracepoint_query (own_buf))
     return;
 
   /* Otherwise we didn't know what packet it was.  Say we didn't
@@ -2533,6 +2543,8 @@ main (int argc, char *argv[])
 	}
       else if (strcmp (*next_arg, "--once") == 0)
 	run_once = 1;
+      else if (strcmp (*next_arg, "--disable-tracepoints") == 0)
+	disable_tracepoints = 1;
       else
 	{
 	  fprintf (stderr, "Unknown argument: %s\n", *next_arg);
@@ -2585,7 +2597,7 @@ main (int argc, char *argv[])
   initialize_inferiors ();
   initialize_async_io ();
   initialize_low ();
-  if (target_supports_tracepoints ())
+  if (support_tracepoints_p ())
     initialize_tracepoint ();
 
   own_buf = xmalloc (PBUFSIZ + 1);