gdbserver: fix silent error exit

Running gdb.threads/process-dies-while-handling-bp.exp against
gdbserver sometimes FAILs because GDBserver drops the connection, but
the logs leave no clue on what the reason could be.  Running manually
a few times, I saw the same:

 $  ./gdbserver/gdbserver --multi :9999 testsuite/gdb.threads/process-dies-while-handling-bp
 Process testsuite/gdb.threads/process-dies-while-handling-bp created; pid = 12766
 Listening on port 9999
 Remote debugging from host 127.0.0.1
 Listening on port 9999

 Child exited with status 0

 Child exited with status 0

What happened is that an exception escaped and gdbserver reopened the
connection, which led to that second "Listening on port 9999" output.

The error was a failure to access registers from a now-dead thread.
The exception probably shouldn't have escaped here, but meanwhile,
this at least makes the issue less mysterious.

Tested on x86_64 Fedora 20.

gdb/gdbserver/ChangeLog:
2015-08-06  Pedro Alves  <palves@redhat.com>

	* server.c (captured_main): On error, print the exception message
	to stderr, and if run_once is set, throw a quit.

2 files changed, 11 insertions, 0 deletions

diff --git a/gdb/gdbserver/ChangeLog b/gdb/gdbserver/ChangeLog
index fe31f73..1c1bb5e 100644
--- a/gdb/gdbserver/ChangeLog
+++ b/gdb/gdbserver/ChangeLog
@@ -1,5 +1,10 @@
 2015-08-06  Pedro Alves  <palves@redhat.com>
 
+	* server.c (captured_main): On error, print the exception message
+	to stderr, and if run_once is set, throw a quit.
+
+2015-08-06  Pedro Alves  <palves@redhat.com>
+
 	* linux-low.c (move_out_of_jump_pad_callback): Temporarily switch
 	the current thread.
 
diff --git a/gdb/gdbserver/server.c b/gdb/gdbserver/server.c
index f15b7be..d3cc0f8 100644
--- a/gdb/gdbserver/server.c
+++ b/gdb/gdbserver/server.c
@@ -3610,11 +3610,17 @@ captured_main (int argc, char *argv[])
 	}
       CATCH (exception, RETURN_MASK_ERROR)
 	{
+	  fflush (stdout);
+	  fprintf (stderr, "gdbserver: %s\n", exception.message);
+
 	  if (response_needed)
 	    {
 	      write_enn (own_buf);
 	      putpkt (own_buf);
 	    }
+
+	  if (run_once)
+	    throw_quit ("Quit");
 	}
       END_CATCH
     }