Fix -trace-save crash when argument is missing

-trace-save doesn't check whether an argument is passed, leading to a
segfault if you pass nothing.

I added a small test, which only tests the error conditions of
-trace-save.

gdb/ChangeLog:

	* mi/mi-main.c (mi_cmd_trace_save): Check if argument is present
	before using it.

gdb/testsuite/ChangeLog:

	* gdb.trace/mi-trace-save.exp: New file.

1 files changed, 42 insertions, 0 deletions

diff --git a/gdb/testsuite/gdb.trace/mi-trace-save.exp b/gdb/testsuite/gdb.trace/mi-trace-save.exp
new file mode 100644
index 0000000..96bb70d
--- /dev/null
+++ b/gdb/testsuite/gdb.trace/mi-trace-save.exp
@@ -0,0 +1,42 @@
+# 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/>.
+
+# The -trace-save command is already tested in other files (e.g.
+# mi-trace-frame-collected.exp), so this file currently only tests the error
+# cases of -trace-save.
+
+load_lib mi-support.exp
+
+mi_gdb_start
+
+# Test without the required "filename" argument.
+
+proc test_trace_save_wrong_num_args { } {
+    set err_re [string_to_regexp "^error,msg=\"Exactly one argument required (file in which to save trace data)\""]
+
+    mi_gdb_test "-trace-save" "$err_re" "-trace-save with missing argument"
+    mi_gdb_test "-trace-save a b" "$err_re" "-trace-save with missing argument"
+}
+
+# Test with an unrecognized option.
+
+proc test_trace_save_wrong_opt { } {
+    set err_re [string_to_regexp "^error,msg=\"-trace-save: Unknown option ``hey''\""]
+
+    mi_gdb_test "-trace-save -hey" "$err_re" "-trace-save with wrong option"
+}
+
+test_trace_save_wrong_num_args
+test_trace_save_wrong_opt