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, 38 insertions, 13 deletions

diff --git a/gdb/record-btrace.c b/gdb/record-btrace.c
index 24594a9..4a51b8e 100644
--- a/gdb/record-btrace.c
+++ b/gdb/record-btrace.c
@@ -21,6 +21,7 @@
 
 #include "defs.h"
 #include "record.h"
+#include "record-btrace.h"
 #include "gdbthread.h"
 #include "target.h"
 #include "gdbcmd.h"
@@ -199,6 +200,26 @@ record_btrace_handle_async_inferior_event (gdb_client_data data)
   inferior_event_handler (INF_REG_EVENT, NULL);
 }
 
+/* See record-btrace.h.  */
+
+void
+record_btrace_push_target (void)
+{
+  const char *format;
+
+  record_btrace_auto_enable ();
+
+  push_target (&record_btrace_ops);
+
+  record_btrace_async_inferior_event_handler
+    = create_async_event_handler (record_btrace_handle_async_inferior_event,
+				  NULL);
+  record_btrace_generating_corefile = 0;
+
+  format = btrace_format_short_string (record_btrace_conf.format);
+  observer_notify_record_changed (current_inferior (), 1, "btrace", format);
+}
+
 /* The to_open method of target record-btrace.  */
 
 static void
@@ -206,7 +227,6 @@ record_btrace_open (const char *args, int from_tty)
 {
   struct cleanup *disable_chain;
   struct thread_info *tp;
-  const char *format;
 
   DEBUG ("open");
 
@@ -226,17 +246,7 @@ record_btrace_open (const char *args, int from_tty)
 	make_cleanup (record_btrace_disable_callback, tp);
       }
 
-  record_btrace_auto_enable ();
-
-  push_target (&record_btrace_ops);
-
-  record_btrace_async_inferior_event_handler
-    = create_async_event_handler (record_btrace_handle_async_inferior_event,
-				  NULL);
-  record_btrace_generating_corefile = 0;
-
-  format = btrace_format_short_string (record_btrace_conf.format);
-  observer_notify_record_changed (current_inferior (), 1, "btrace", format);
+  record_btrace_push_target ();
 
   discard_cleanups (disable_chain);
 }
@@ -257,6 +267,21 @@ record_btrace_stop_recording (struct target_ops *self)
       btrace_disable (tp);
 }
 
+/* The to_disconnect method of target record-btrace.  */
+
+static void
+record_btrace_disconnect (struct target_ops *self, const char *args,
+			  int from_tty)
+{
+  struct target_ops *beneath = self->beneath;
+
+  /* Do not stop recording, just clean up GDB side.  */
+  unpush_target (self);
+
+  /* Forward disconnect.  */
+  beneath->to_disconnect (beneath, args, from_tty);
+}
+
 /* The to_close method of target record-btrace.  */
 
 static void
@@ -2824,7 +2849,7 @@ init_record_btrace_ops (void)
   ops->to_close = record_btrace_close;
   ops->to_async = record_btrace_async;
   ops->to_detach = record_detach;
-  ops->to_disconnect = record_disconnect;
+  ops->to_disconnect = record_btrace_disconnect;
   ops->to_mourn_inferior = record_mourn_inferior;
   ops->to_kill = record_kill;
   ops->to_stop_recording = record_btrace_stop_recording;