[PATCH] Fix error when gdb connect to a stub that tracepoint is running[1/2] reset current_trace_status in the begin of remote_start_remote

[Hui Zhu <hui_zhu@mentor.com>]

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Hi,

For the re-insert breakpoint, the stack dump is:
#0  remote_download_tracepoint (loc=0x35040b0) at 
../../src/gdb/remote.c:9982
#1  0x00000000006727c1 in download_tracepoint_locations () at 
../../src/gdb/breakpoint.c:10670
#2  0x0000000000673111 in update_global_location_list (should_insert=1) 
at ../../src/gdb/breakpoint.c:11021
#3  0x0000000000663752 in create_overlay_event_breakpoint () at 
../../src/gdb/breakpoint.c:2322
#4  0x0000000000675c9f in breakpoint_re_set () at 
../../src/gdb/breakpoint.c:12621
#5  0x00000000007efe65 in solib_add (pattern=0x0, from_tty=1, 
target=0x1d1e860, readsyms=1)
     at ../../src/gdb/solib.c:928
#6  0x000000000057b452 in enable_break (info=0x3307890, from_tty=1) at 
../../src/gdb/solib-svr4.c:1624
#7  0x000000000057c428 in svr4_solib_create_inferior_hook (from_tty=1) 
at ../../src/gdb/solib-svr4.c:2234
#8  0x00000000007f04a9 in solib_create_inferior_hook (from_tty=1) at 
../../src/gdb/solib.c:1172
#9  0x00000000006cc8e5 in post_create_inferior (target=0x1d1e860, 
from_tty=1) at ../../src/gdb/infcmd.c:431
#10 0x00000000006d479d in start_remote (from_tty=1) at 
../../src/gdb/infrun.c:2309
#11 0x00000000005d80c9 in remote_start_remote (from_tty=1, 
target=0x1cefce0, extended_p=0)
     at ../../src/gdb/remote.c:3367

About this patch, what I do is:
1. If we try to connect an new stub, reset current_trace_status to unknown.
2. Change remote_can_download_tracepoint to if the current_trace_status 
is unknown, return false.
After this patch, the tracepoint insered after:
   /* Possibly the target has been engaged in a trace run started
      previously; find out where things are at.  */
   if (remote_get_trace_status (current_trace_status ()) != -1)
     {
I think that will make us handle tracepoint issue more easy.

2012-01-31  Hui Zhu  <hui_zhu@mentor.com>

	* remote.c (remote_start_remote): Set running_known of
	current_trace_status to 0 in the begin of this function.
	(remote_can_download_tracepoint): If running_known of
	current_trace_status is 0, return false.

Thanks,
Hui

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---
 remote.c |   13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

--- a/remote.c
+++ b/remote.c
@@ -3203,6 +3203,7 @@ remote_start_remote (int from_tty, struc
   struct remote_state *rs = get_remote_state ();
   struct packet_config *noack_config;
   char *wait_status = NULL;
+  struct trace_status *ts = current_trace_status ();
 
   immediate_quit++;		/* Allow user to interrupt it.  */
 
@@ -3212,6 +3213,9 @@ remote_start_remote (int from_tty, struc
   /* Ack any packet which the remote side has already sent.  */
   serial_write (remote_desc, "+", 1);
 
+  /* Clear current status of trace.  */
+  ts->running_known = 0;
+
   /* The first packet we send to the target is the optional "supported
      packets" request.  If the target can answer this, it will tell us
      which later probes to skip.  */
@@ -10122,9 +10126,14 @@ static int
 remote_can_download_tracepoint (void)
 {
   struct trace_status *ts = current_trace_status ();
-  int status = remote_get_trace_status (ts);
+  int status;
 
-  if (status == -1 || !ts->running_known || !ts->running)
+  if (!ts->running_known)
+    return 0;
+
+  status = remote_get_trace_status (ts);
+
+  if (status == -1 || !ts->running)
     return 0;
 
   /* If we are in a tracing experiment, but remote stub doesn't support