Fix crash in gdbpy_parse_register_id

I noticed that gdbpy_parse_register_id would assert if passed a Python
object of a type it was not expecting.  The included test case shows
this crash.  This patch fixes the problem and also changes
gdbpy_parse_register_id to be more "Python-like" -- it always ensures
the Python error is set when it fails, and the callers now simply
propagate the existing exception.

gdb/python/py-frame.c

@@ -253,10 +253,7 @@ frapy_read_register (PyObject *self, PyObject *args)
 
       if (!gdbpy_parse_register_id (get_frame_arch (frame), pyo_reg_id,
 				    &regnum))
-	{
-	  PyErr_SetString (PyExc_ValueError, "Bad register");
-	  return NULL;
-	}
+	return nullptr;
 
       gdb_assert (regnum >= 0);
       val = value_of_register (regnum, frame);

gdb/python/py-registers.c

@@ -381,21 +381,27 @@ gdbpy_parse_register_id (struct gdbarch *gdbarch, PyObject *pyo_reg_id,
 	{
 	  *reg_num = user_reg_map_name_to_regnum (gdbarch, reg_name.get (),
 						  strlen (reg_name.get ()));
-	  return *reg_num >= 0;
+	  if (*reg_num >= 0)
+	    return true;
+	  PyErr_SetString (PyExc_ValueError, "Bad register");
 	}
     }
   /* The register could be its internal GDB register number.  */
   else if (PyLong_Check (pyo_reg_id))
     {
       long value;
-      if (gdb_py_int_as_long (pyo_reg_id, &value) && (int) value == value)
+      if (gdb_py_int_as_long (pyo_reg_id, &value) == 0)
 	{
-	  if (user_reg_map_regnum_to_name (gdbarch, value) != NULL)
-	    {
-	      *reg_num = (int) value;
-	      return true;
-	    }
+	  /* Nothing -- error.  */
 	}
+      else if ((int) value == value
+	       && user_reg_map_regnum_to_name (gdbarch, value) != NULL)
+	{
+	  *reg_num = (int) value;
+	  return true;
+	}
+      else
+	PyErr_SetString (PyExc_ValueError, "Bad register");
     }
   /* The register could be a gdb.RegisterDescriptor object.  */
   else if (PyObject_IsInstance (pyo_reg_id,
@@ -412,6 +418,8 @@ gdbpy_parse_register_id (struct gdbarch *gdbarch, PyObject *pyo_reg_id,
 	PyErr_SetString (PyExc_ValueError,
 			 _("Invalid Architecture in RegisterDescriptor"));
     }
+  else
+    PyErr_SetString (PyExc_TypeError, _("Invalid type for register"));
 
   gdb_assert (PyErr_Occurred ());
   return false;

gdb/python/py-unwind.c

@@ -260,10 +260,7 @@ unwind_infopy_add_saved_register (PyObject *self, PyObject *args)
 			  &pyo_reg_id, &pyo_reg_value))
     return NULL;
   if (!gdbpy_parse_register_id (pending_frame->gdbarch, pyo_reg_id, &regnum))
-    {
-      PyErr_SetString (PyExc_ValueError, "Bad register");
-      return NULL;
-    }
+    return nullptr;
 
   /* If REGNUM identifies a user register then *maybe* we can convert this
      to a real (i.e. non-user) register.  The maybe qualifier is because we
@@ -381,10 +378,7 @@ pending_framepy_read_register (PyObject *self, PyObject *args)
   if (!PyArg_UnpackTuple (args, "read_register", 1, 1, &pyo_reg_id))
     return NULL;
   if (!gdbpy_parse_register_id (pending_frame->gdbarch, pyo_reg_id, &regnum))
-    {
-      PyErr_SetString (PyExc_ValueError, "Bad register");
-      return NULL;
-    }
+    return nullptr;
 
   try
     {

gdb/python/python-internal.h

@@ -819,7 +819,8 @@ typedef std::unique_ptr<Py_buffer, Py_buffer_deleter> Py_buffer_up;
 
    If a register is parsed successfully then *REG_NUM will have been
    updated, and true is returned.  Otherwise the contents of *REG_NUM are
-   undefined, and false is returned.
+   undefined, and false is returned.  When false is returned, the
+   Python error is set.
 
    The PYO_REG_ID object can be a string, the name of the register.  This
    is the slowest approach as GDB has to map the name to a number for each