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.

gdb/ChangeLog

@@ -1,3 +1,8 @@
+2016-10-17  Simon Marchi  <simon.marchi@ericsson.com>
+
+	* mi/mi-main.c (mi_cmd_trace_save): Check if argument is present
+	before using it.
+
 2016-10-17  Pedro Alves  <palves@redhat.com>
 
 	* charset.h (class wchar_iterator) [PHONY_ICONV] <m_desc>: Use

gdb/mi/mi-main.c

@@ -2699,6 +2699,11 @@ mi_cmd_trace_save (char *command, char **argv, int argc)
 	  break;
 	}
     }
+
+  if (argc - oind != 1)
+    error (_("Exactly one argument required "
+	     "(file in which to save trace data)"));
+
   filename = argv[oind];
 
   if (generate_ctf)

gdb/testsuite/ChangeLog

@@ -1,3 +1,7 @@
+2016-10-17  Simon Marchi  <simon.marchi@ericsson.com>
+
+	* gdb.trace/mi-trace-save.exp: New file.
+
 2016-10-13  Yao Qi  <yao.qi@linaro.org>
 
 	* gdb.base/code_elim.exp (get_var_address): Remove.

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