Add support for writing unwinders in Python.

gdb/ChangeLog:

	* Makefile.in (SUBDIR_PYTHON_OBJS): Add py-unwind.o.
	(SUBDIR_PYTHON_SRCS): Add py-unwind.c.
	(py-unwind.o): New recipe.
	* NEWS: mention Python frame unwinding.
	* data-directory/Makefile.in (PYTHON_FILE_LIST): Add
	gdb/unwinder.py and gdb/command/unwinder.py
	* python/lib/gdb/__init__.py (packages): Add frame_unwinders
	list.
	(execute_unwinders): New function.
	* python/lib/gdb/command/unwinders.py: New file.
	* python/lib/gdb/unwinder.py: New file.
	* python/py-objfile.c (objfile_object): Add frame_unwinders field.
	(objfpy_dealloc): Decrement frame_unwinders reference count.
	(objfpy_initialize): Create frame_unwinders list.
	(objfpy_get_frame_unwinders): New function.
	(objfpy_set_frame_unwinders): Ditto.
	(objfile_getset): Add frame_unwinders attribute to Objfile.
	* python/py-progspace.c (pspace_object): Add frame_unwinders field.
	(pspy_dealloc): Decrement frame_unwinders reference count.
	(pspy_initialize): Create frame_unwinders list.
	(pspy_get_frame_unwinders): New function.
	(pspy_set_frame_unwinders): Ditto.
	(pspy_getset): Add frame_unwinders attribute to gdb.Progspace.
	* python/py-unwind.c: New file.
	* python/python-internal.h (pspy_get_name_unwinders): New prototype.
	(objpy_get_frame_unwinders): New prototype.
	(gdbpy_initialize_unwind): New prototype.
	* python/python.c (gdbpy_apply_type_printers): Call
	gdbpy_initialize_unwind.

gdb/doc/ChangeLog:

	* doc/python.texi (Writing a Frame Unwinder in Python): Add
	section.

gdb/testsuite/ChangeLog:

	* gdb.python/py-unwind-maint.c: New file.
	* gdb.python/py-unwind-maint.exp: New test.
	* gdb.python/py-unwind-maint.py: New file.
	* gdb.python/py-unwind.c: New file.
	* gdb.python/py-unwind.exp: New test.
	* gdb.python/py-unwind.py: New test.

gdb/python/py-objfile.c

@@ -42,6 +42,10 @@ typedef struct
 
   /* The frame filter list of functions.  */
   PyObject *frame_filters;
+
+  /* The list of frame unwinders.  */
+  PyObject *frame_unwinders;
+
   /* The type-printer list.  */
   PyObject *type_printers;
 
@@ -184,6 +188,7 @@ objfpy_dealloc (PyObject *o)
   Py_XDECREF (self->dict);
   Py_XDECREF (self->printers);
   Py_XDECREF (self->frame_filters);
+  Py_XDECREF (self->frame_unwinders);
   Py_XDECREF (self->type_printers);
   Py_XDECREF (self->xmethods);
   Py_TYPE (self)->tp_free (self);
@@ -206,6 +211,10 @@ objfpy_initialize (objfile_object *self)
   if (self->frame_filters == NULL)
     return 0;
 
+  self->frame_unwinders = PyList_New (0);
+  if (self->frame_unwinders == NULL)
+    return 0;
+
   self->type_printers = PyList_New (0);
   if (self->type_printers == NULL)
     return 0;
@@ -313,6 +322,48 @@ objfpy_set_frame_filters (PyObject *o, PyObject *filters, void *ignore)
   return 0;
 }
 
+/* Return the frame unwinders attribute for this object file.  */
+
+PyObject *
+objfpy_get_frame_unwinders (PyObject *o, void *ignore)
+{
+  objfile_object *self = (objfile_object *) o;
+
+  Py_INCREF (self->frame_unwinders);
+  return self->frame_unwinders;
+}
+
+/* Set this object file's frame unwinders list to UNWINDERS.  */
+
+static int
+objfpy_set_frame_unwinders (PyObject *o, PyObject *unwinders, void *ignore)
+{
+  PyObject *tmp;
+  objfile_object *self = (objfile_object *) o;
+
+  if (!unwinders)
+    {
+      PyErr_SetString (PyExc_TypeError,
+		       _("Cannot delete the frame unwinders attribute."));
+      return -1;
+    }
+
+  if (!PyList_Check (unwinders))
+    {
+      PyErr_SetString (PyExc_TypeError,
+		       _("The frame_unwinders attribute must be a list."));
+      return -1;
+    }
+
+  /* Take care in case the LHS and RHS are related somehow.  */
+  tmp = self->frame_unwinders;
+  Py_INCREF (unwinders);
+  self->frame_unwinders = unwinders;
+  Py_XDECREF (tmp);
+
+  return 0;
+}
+
 /* Get the 'type_printers' attribute.  */
 
 static PyObject *
@@ -651,6 +702,8 @@ static PyGetSetDef objfile_getset[] =
     "Pretty printers.", NULL },
   { "frame_filters", objfpy_get_frame_filters,
     objfpy_set_frame_filters, "Frame Filters.", NULL },
+  { "frame_unwinders", objfpy_get_frame_unwinders,
+    objfpy_set_frame_unwinders, "Frame Unwinders", NULL },
   { "type_printers", objfpy_get_type_printers, objfpy_set_type_printers,
     "Type printers.", NULL },
   { "xmethods", objfpy_get_xmethods, NULL,