gdb/testsuite/fortran: Add mixed language stack test

This commit adds a test that builds a mixed language stack, the stack
contains frames of Fortran, C, and C++.  The test prints the backtrace
and explores the stack printing arguments of different types in frames
of different languages.

The core of the test is repeated with GDB's language set to auto,
fortran, c, and c++ in turn to ensure that GDB is happy to print
frames and frame arguments when the language is set to a value that
doesn't match the frame language.

This test currently passes, and there are no known bugs in this area.
The aim of this commit is simply to increase test coverage, as I don't
believe this functionality is currently tested.

gdb/testsuite/ChangeLog:

	* gdb.fortran/mixed-lang-stack.c: New file.
	* gdb.fortran/mixed-lang-stack.cpp: New file.
	* gdb.fortran/mixed-lang-stack.exp: New file.
	* gdb.fortran/mixed-lang-stack.f90: New file.

1 files changed, 85 insertions, 0 deletions

diff --git a/gdb/testsuite/gdb.fortran/mixed-lang-stack.cpp b/gdb/testsuite/gdb.fortran/mixed-lang-stack.cpp
new file mode 100644
index 0000000..0e49e8e
--- /dev/null
+++ b/gdb/testsuite/gdb.fortran/mixed-lang-stack.cpp
@@ -0,0 +1,85 @@
+/* Copyright 2020 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 2 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 <cstring>
+#include <cstdlib>
+
+class base_one
+{
+  int num1 = 1;
+  int num2 = 2;
+  int num3 = 3;
+};
+
+class base_two
+{
+public:
+  base_two ()
+  {
+    string = strdup ("Something in C++");
+  }
+
+  ~base_two ()
+  {
+    free (string);
+  }
+
+  char *string = nullptr;
+  float val = 3.5;
+};
+
+class derived_type : public base_one, base_two
+{
+public:
+  derived_type ()
+    : base_one (),
+      base_two ()
+  {
+    /* Nothing.  */
+  }
+
+private:
+  int xxx = 9;
+  float yyy = 10.5;
+};
+
+static void mixed_func_1f ();
+static void mixed_func_1g ();
+
+extern "C"
+{
+  /* Entry point to be called from Fortran. */
+  void
+  mixed_func_1e ()
+  {
+    mixed_func_1f ();
+  }
+
+  /* The entry point back into Fortran.  */
+  extern void mixed_func_1h_ ();
+}
+
+static void
+mixed_func_1g (derived_type obj)
+{
+  mixed_func_1h_ ();
+}
+
+static void
+mixed_func_1f () {
+  derived_type obj;
+
+  mixed_func_1g (obj);
+}