Python: Use correct ptid in btrace recording

The user would always get the instruction_history and function_call_history
objects of the current thread, not the thread for which the gdb.Record object
was created.

The attached testcase fails without this patch and passes with the patch.

gdb/testsuite/gdb.python/py-record-btrace-threads.c

@@ -0,0 +1,58 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2017 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 <pthread.h>
+
+static pthread_barrier_t barrier;
+static int dummy;
+
+static void *
+func1 (void *arg)
+{
+  pthread_barrier_wait (&barrier);
+  dummy = 1; /* bp1 */
+  pthread_barrier_wait (&barrier);
+  dummy = 1;
+  pthread_barrier_wait (&barrier);
+  return arg;
+}
+
+static void *
+func2 (void *arg)
+{
+  pthread_barrier_wait (&barrier);
+  dummy = 2;
+  pthread_barrier_wait (&barrier);
+  dummy = 2;
+  pthread_barrier_wait (&barrier); /* bp2 */
+  return arg;
+}
+
+int
+main (void)
+{
+  pthread_t thread;
+
+  pthread_barrier_init (&barrier, NULL, 2);
+
+  pthread_create (&thread, NULL, func2, NULL);
+  func1 (NULL);
+
+  pthread_join (thread, NULL);
+  pthread_barrier_destroy (&barrier);
+  return 0;
+}

gdb/testsuite/gdb.python/py-record-btrace-threads.exp

@@ -0,0 +1,81 @@
+# This testcase is part of GDB, the GNU debugger.
+#
+# Copyright 2017 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/>.
+
+# Skip this test if btrace is disabled.
+
+if { [skip_btrace_tests] } {
+    untested "skipping btrace tests"
+    return -1
+}
+
+standard_testfile
+
+if { [gdb_compile_pthreads "$srcdir/$subdir/$srcfile" "$binfile" executable {debug} ] != "" } {
+    untested "failed to prepare"
+    return -1
+}
+clean_restart $testfile
+
+# Skip this test if python is disabled.
+
+load_lib gdb-python.exp
+if { [skip_python_tests] } {
+    untested "skipping python tests"
+    return -1
+}
+
+if { ![runto_main] } {
+    untested "failed to run to main"
+    return -1
+}
+
+# set up breakpoints
+gdb_breakpoint $srcfile:[gdb_get_line_number "bp1" $srcfile]
+gdb_breakpoint $srcfile:[gdb_get_line_number "bp2" $srcfile]
+
+# record data
+gdb_continue_to_breakpoint "cont to bp.1" ".*bp1.*"
+gdb_test_no_output "record btrace"
+gdb_continue_to_breakpoint "cont to bp.2" ".*bp2.*"
+
+# acquire the record objects for thread 1 and thread 2
+gdb_test "thread 1" ".*"
+gdb_test "record function-call-history" ".*" "fch thread 1"
+gdb_test_no_output "python rec1 = gdb.current_recording()"
+gdb_test "thread 2" ".*"
+gdb_test "record function-call-history" ".*" "fch thread 2"
+gdb_test_no_output "python rec2 = gdb.current_recording()"
+
+# Thread 1 is supposed to call func1 (), thread 2 is supposed to call func2 ().
+# Check that the function call history for the current thread contains a call
+# to the right function and does not contain a call to the wrong function.
+proc check_insn_for_thread { self other } {
+  with_test_prefix "checking thread $self" {
+    gdb_test_no_output "python fch = rec$self.function_call_history"
+    gdb_test_no_output "python f1calls = \{x for x in fch if x.symbol and x.symbol.name == \"func1\"\}"
+    gdb_test_no_output "python f2calls = \{x for x in fch if x.symbol and x.symbol.name == \"func2\"\}"
+
+    gdb_test "python print not f${self}calls" "False"
+    gdb_test "python print not f${other}calls" "True"
+  }
+}
+
+foreach_with_prefix thread { 1 2 } {
+  gdb_test "thread $thread"
+  check_insn_for_thread 1 2
+  check_insn_for_thread 2 1
+}