[PATCH] Prevent turning record on while threads are running (PR 20869)

[Simon Marchi <simon dot marchi at ericsson dot com>]

As stated in the bug description, trying to do "record" while threads
are running leads to a broken state.  I tried to see in the code if
there was anything to try to support the use case of enabling record
while the program is running, but didn't find anything.

When full/software recording is active, we are single stepping each
instruction.  Transitioning from the state where threads are running
freely (no recording) to recording enabled should therefore involve a
step where we stop them to initiate the single stepping.  I can't find
anything that looks like this, so my conclusion is that this was never a
supported use case (please correct me if I'm wrong).

The easy solution is to prevent the user for enabling record if a thread
is running.

I also wanted to know whether it was supported to start btrace bts/pt
recording with threads running.  When I try it with btrace bts, it works
halfway.  "record btrace bts" gives me the error:

  Couldn't get registers: No such process.

If I do the command again, gdb doesn't complain and then I'm able to
interrupt the target and use reverse-next.  However, since the
initialization function was interrupted halfway, I am not sure that
everything is setup correctly.  If we want to allow it, we would first
need to look into this issue.

I have therefore put a check for running threads in record_preopen,
which affects all recording methods.  It can always be moved to
record_full_open if we only want to affect record full.

No regression on the buildbot.

gdb/ChangeLog:

	* record.c: Include gdbthread.h.
	(record_preopen): Check if any thread is running.

gdb/testsuite:

	* gdb.reverse/record-while-running.c: New file.
	* gdb.reverse/record-while-running.exp: New file.
---
 gdb/record.c                                       | 11 ++++++
 gdb/testsuite/gdb.reverse/record-while-running.c   | 29 ++++++++++++++++
 gdb/testsuite/gdb.reverse/record-while-running.exp | 40 ++++++++++++++++++++++
 3 files changed, 80 insertions(+)
 create mode 100644 gdb/testsuite/gdb.reverse/record-while-running.c
 create mode 100644 gdb/testsuite/gdb.reverse/record-while-running.exp

diff --git a/gdb/record.c b/gdb/record.c
index 34ebd1b..e0bc133 100644
--- a/gdb/record.c
+++ b/gdb/record.c
@@ -26,6 +26,7 @@
 #include "common/common-utils.h"
 #include "cli/cli-utils.h"
 #include "disasm.h"
+#include "gdbthread.h"
 
 #include <ctype.h>
 
@@ -89,6 +90,16 @@ record_preopen (void)
   if (find_record_target () != NULL)
     error (_("The process is already being recorded.  Use \"record stop\" to "
 	     "stop recording first."));
+
+  iterate_over_threads([] (struct thread_info *tp, void *) -> int {
+    if (tp->state == thread_state::THREAD_RUNNING)
+      error (_ ("Can't enable record while the program is running.  Use "
+		"\"interrupt\" to stop it first."));
+
+    return 0;
+  }, NULL);
+
+
 }
 
 /* See record.h.  */
diff --git a/gdb/testsuite/gdb.reverse/record-while-running.c b/gdb/testsuite/gdb.reverse/record-while-running.c
new file mode 100644
index 0000000..f00ceb6
--- /dev/null
+++ b/gdb/testsuite/gdb.reverse/record-while-running.c
@@ -0,0 +1,29 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2016 Free Software Foundation, Inc.
+
+   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/>.  */
+
+#include <unistd.h>
+
+int
+main ()
+{
+   int i;
+
+   for (i = 0; i < 30; i++)
+      sleep (1);
+
+   return 0;
+}
diff --git a/gdb/testsuite/gdb.reverse/record-while-running.exp b/gdb/testsuite/gdb.reverse/record-while-running.exp
new file mode 100644
index 0000000..57e1df3
--- /dev/null
+++ b/gdb/testsuite/gdb.reverse/record-while-running.exp
@@ -0,0 +1,40 @@
+# Copyright 2016 Free Software Foundation, Inc.
+
+# 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/>.  */
+
+# Test that trying to turn on recording while the target is running is correctly
+# handled.
+
+if ![supports_reverse] {
+    return
+}
+
+standard_testfile
+
+if { [prepare_for_testing $testfile.exp $testfile $srcfile] } {
+    fail "failed to compile"
+    return
+}
+
+if { ![runto_main] } {
+    fail "couldn't run to main"
+    return
+}
+
+proc test_record_while_running { } {
+    gdb_test "continue &" "Continuing."
+    gdb_test "record" "Can't enable record while the program is running.  Use \"interrupt\" to stop it first."
+}
+
+test_record_while_running
-- 
2.10.2