[PATCH v4 1/1] btrace: Resume recording after disconnect.

[Tim Wiederhake <tim dot wiederhake at intel dot com>]

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

2016-07-22  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.


---
 gdb/NEWS                               |  3 ++
 gdb/doc/gdb.texinfo                    |  4 +-
 gdb/record-btrace.c                    | 51 ++++++++++++++++------
 gdb/record-btrace.h                    | 28 ++++++++++++
 gdb/remote.c                           | 61 ++++++++++++++++++++++++++
 gdb/testsuite/gdb.btrace/reconnect.c   | 25 +++++++++++
 gdb/testsuite/gdb.btrace/reconnect.exp | 79 ++++++++++++++++++++++++++++++++++
 7 files changed, 237 insertions(+), 14 deletions(-)
 create mode 100644 gdb/record-btrace.h
 create mode 100644 gdb/testsuite/gdb.btrace/reconnect.c
 create mode 100644 gdb/testsuite/gdb.btrace/reconnect.exp

diff --git a/gdb/NEWS b/gdb/NEWS
index c29e69a..721bed8 100644
--- a/gdb/NEWS
+++ b/gdb/NEWS
@@ -3,6 +3,9 @@
 
 *** Changes since GDB 7.11
 
+* GDBserver now supports recording btrace without maintaining an active
+  GDB connection.
+
 * GDB now supports a negative repeat count in the 'x' command to examine
   memory backward from the given address.  For example:
 
diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index a068622..6e2cebf 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -6631,7 +6631,9 @@ Hardware-supported instruction recording.  This method does not record
 data.  Further, the data is collected in a ring buffer so old data will
 be overwritten when the buffer is full.  It allows limited reverse
 execution.  Variables and registers are not available during reverse
-execution.
+execution.  In remote debugging, recording continues on disconnect.
+Recorded data can be inspected after reconnecting.  The recording may
+be stopped using @code{record stop}.
 
 The recording format can be specified as parameter.  Without a parameter
 the command chooses the recording format.  The following recording
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;
diff --git a/gdb/record-btrace.h b/gdb/record-btrace.h
new file mode 100644
index 0000000..d2062b8
--- /dev/null
+++ b/gdb/record-btrace.h
@@ -0,0 +1,28 @@
+/* Branch trace support for GDB, the GNU debugger.
+
+   Copyright (C) 2016 Free Software Foundation, Inc.
+
+   Contributed by Intel Corp. <tim.wiederhake@intel.com>
+
+   This file is part of GDB.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+#ifndef RECORD_BTRACE_H
+#define RECORD_BTRACE_H
+
+/* Push the record_btrace target.  */
+extern void record_btrace_push_target (void);
+
+#endif /* RECORD_BTRACE_H */
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 *
diff --git a/gdb/testsuite/gdb.btrace/reconnect.c b/gdb/testsuite/gdb.btrace/reconnect.c
new file mode 100644
index 0000000..f2a9d35
--- /dev/null
+++ b/gdb/testsuite/gdb.btrace/reconnect.c
@@ -0,0 +1,25 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2016 Free Software Foundation, Inc.
+
+   Contributed by Intel Corp. <tim.wiederhake@intel.com>
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+
+int
+main (void)
+{
+  return 0;
+}
diff --git a/gdb/testsuite/gdb.btrace/reconnect.exp b/gdb/testsuite/gdb.btrace/reconnect.exp
new file mode 100644
index 0000000..485a4df
--- /dev/null
+++ b/gdb/testsuite/gdb.btrace/reconnect.exp
@@ -0,0 +1,79 @@
+# This testcase is part of GDB, the GNU debugger.
+#
+# Copyright 2016 Free Software Foundation, Inc.
+#
+# Contributed by Intel Corp. <tim.wiederhake@intel.com>
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+load_lib gdbserver-support.exp
+
+if { [skip_btrace_tests] } { return -1 }
+if { [skip_gdbserver_tests] } { return -1 }
+
+standard_testfile
+if [prepare_for_testing $testfile.exp $testfile $srcfile] {
+    return -1
+}
+
+# Make sure we're disconnected and no recording is active, in case
+# we're testing with an extended-remote board, therefore already
+# connected.
+with_test_prefix "preparation" {
+  gdb_test "record stop" ".*"
+  gdb_test "disconnect" ".*"
+}
+
+# Start fresh gdbserver.
+set gdbserver_reconnect_p 1
+set res [gdbserver_start "" $binfile]
+set gdbserver_protocol [lindex $res 0]
+set gdbserver_gdbport [lindex $res 1]
+gdb_target_cmd $gdbserver_protocol $gdbserver_gdbport
+
+# Create a record, check, reconnect
+with_test_prefix "first" {
+  gdb_test_no_output "record btrace" "record btrace enable"
+  gdb_test "stepi 19" "0x.* in .* from target.*"
+
+  gdb_test "info record" [multi_line \
+    "Active record target: .*" \
+    "Recorded 19 instructions in .+ functions \\(. gaps\\) for thread 1 \\(Thread .*\\)."
+  ]
+
+  gdb_test "disconnect" "Ending remote debugging."
+  gdb_target_cmd $gdbserver_protocol $gdbserver_gdbport
+}
+
+# Test if we can access the recorded data from first connect.
+# Note: BTS loses the first function call entry with its associated
+# instructions for technical reasons.  This is why we test for
+# "a number between 10 and 19", so we catch at least the case where
+# there are 0 instructions in the record.
+with_test_prefix "second" {
+  gdb_test "info record" [multi_line \
+    "Active record target: .*" \
+    "Recorded 1. instructions in .+ functions \\(. gaps\\) for thread 1 \\(Thread .*\\)."
+  ]
+
+  gdb_test "record stop" "Process record is stopped and all execution logs are deleted."
+
+  gdb_test "disconnect" "Ending remote debugging."
+  gdb_target_cmd $gdbserver_protocol $gdbserver_gdbport
+}
+
+# Test that recording is now off.
+with_test_prefix "third" {
+  gdb_test "info record" "No record target is currently active."
+}
-- 
2.7.4