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

2 files changed, 104 insertions, 0 deletions

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."
+}