btrace: Resume recording after disconnect.

This patch allows gdbserver to continue recording after disconnect.  On
reconnect, the recorded data is accessible to gdb as if no disconnect happened.

A possible application for this feature is remotely examine bugs that occur
at irregular intervals, where maintaining a gdb connection is inconvenient.

This also fixes the issue mentioned here:
https://sourceware.org/ml/gdb-patches/2015-11/msg00424.html

Signed-off-by: Tim Wiederhake <tim.wiederhake@intel.com>

gdb/ChangeLog:
	* NEWS: Resume btrace on reconnect.
	* record-btrace.c: Added record-btrace.h include.
	(record_btrace_open): Split into this and ...
	(record_btrace_push_target): ... this.
	(record_btrace_disconnect): New function.
	(init_record_btrace_ops): Use record_btrace_disconnect.
	* record-btrace.h: New file.
	* remote.c: Added record-btrace.h include.
	(remote_start_remote): Check recording status.
	(remote_btrace_maybe_reopen): New function.

gdb/doc/ChangeLog:
	* gdb.texinfo: Resume btrace on reconnect.

gdb/testsuite/ChangeLog:

	* gdb.btrace/reconnect.c: New file.
	* gdb.btrace/reconnect.exp: New file.

Change-Id: I95e8b0ab8a89e58591aba0e63818cee82fd211bc

1 files changed, 61 insertions, 0 deletions

diff --git a/gdb/remote.c b/gdb/remote.c
index 5568346..7944983 100644
--- a/gdb/remote.c
+++ b/gdb/remote.c
@@ -70,6 +70,7 @@
 #include "ax-gdb.h"
 #include "agent.h"
 #include "btrace.h"
+#include "record-btrace.h"
 
 /* Temp hacks for tracepoint encoding migration.  */
 static char *target_buf;
@@ -231,6 +232,8 @@ static int remote_can_run_breakpoint_commands (struct target_ops *self);
 
 static void remote_btrace_reset (void);
 
+static void remote_btrace_maybe_reopen (void);
+
 static int stop_reply_queue_length (void);
 
 static void readahead_cache_invalidate (void);
@@ -4298,6 +4301,10 @@ remote_start_remote (int from_tty, struct target_ops *target, int extended_p)
       merge_uploaded_tracepoints (&uploaded_tps);
     }
 
+  /* Possibly the target has been engaged in a btrace record started
+     previously; find out where things are at.  */
+  remote_btrace_maybe_reopen ();
+
   /* The thread and inferior lists are now synchronized with the
      target, our symbols have been relocated, and we're merged the
      target's tracepoints with ours.  We're done with basic start
@@ -12774,6 +12781,60 @@ btrace_read_config (struct btrace_config *conf)
     }
 }
 
+/* Maybe reopen target btrace.  */
+
+static void
+remote_btrace_maybe_reopen (void)
+{
+  struct remote_state *rs = get_remote_state ();
+  struct cleanup *cleanup;
+  struct thread_info *tp;
+  int btrace_target_pushed = 0;
+  int warned = 0;
+
+  cleanup = make_cleanup_restore_current_thread ();
+  ALL_NON_EXITED_THREADS (tp)
+    {
+      set_general_thread (tp->ptid);
+
+      memset (&rs->btrace_config, 0x00, sizeof (struct btrace_config));
+      btrace_read_config (&rs->btrace_config);
+
+      if (rs->btrace_config.format == BTRACE_FORMAT_NONE)
+	continue;
+
+#if !defined (HAVE_LIBIPT)
+      if (rs->btrace_config.format == BTRACE_FORMAT_PT)
+	{
+	  if (!warned)
+	    {
+	      warned = 1;
+	      warning (_("GDB does not support Intel Processor Trace. "
+			 "\"record\" will not work in this session."));
+	    }
+
+	  continue;
+	}
+#endif /* !defined (HAVE_LIBIPT) */
+
+      /* Push target, once, but before anything else happens.  This way our
+	 changes to the threads will be cleaned up by unpushing the target
+	 in case btrace_read_config () throws.  */
+      if (!btrace_target_pushed)
+	{
+	  btrace_target_pushed = 1;
+	  record_btrace_push_target ();
+	  printf_filtered (_("Target is recording using %s.\n"),
+			   btrace_format_string (rs->btrace_config.format));
+	}
+
+      tp->btrace.target = XCNEW (struct btrace_target_info);
+      tp->btrace.target->ptid = tp->ptid;
+      tp->btrace.target->conf = rs->btrace_config;
+    }
+  do_cleanups (cleanup);
+}
+
 /* Enable branch tracing.  */
 
 static struct btrace_target_info *