Add python gdb.GdbError and gdb.string_to_argv.

* NEWS: Document them.
	* python/py-cmd.c (cmdpy_function): Don't print a traceback if
	the exception is gdb.GdbError.  Print a second traceback if there's
	an error computing the error message.
	(gdbpy_string_to_argv): New function.
	* python/py-utils.c (gdbpy_obj_to_string): New function.
	(gdbpy_exception_to_string): New function.
	* python/python-internal.h (gdbpy_string_to_argv): Declare.
	(gdbpy_obj_to_string, gdbpy_exception_to_string): Declare.
	(gdbpy_gdberror_exc): Declare.
	* python/python.c (gdbpy_gdberror_exc): New global.
	(_initialize_python): Initialize gdbpy_gdberror_exc and create
	gdb.GdbError.
	(GdbMethods): Add string_to_argv.

	doc/
	* gdb.texinfo (Exception Handling): Document gdb.GdbError.
	(Commands In Python): Document gdb.string_to_argv.

	testsuite/
	* gdb.python/py-cmd.exp: Add tests for gdb.GdbError and
	gdb.string_to_argv.

gdb/python/py-cmd.c

@@ -88,6 +88,7 @@ cmdpy_dont_repeat (PyObject *self, PyObject *args)
 
 
 /* Called if the gdb cmd_list_element is destroyed.  */
+
 static void
 cmdpy_destroyer (struct cmd_list_element *self, void *context)
 {
@@ -111,6 +112,7 @@ cmdpy_destroyer (struct cmd_list_element *self, void *context)
 }
 
 /* Called by gdb to invoke the command.  */
+
 static void
 cmdpy_function (struct cmd_list_element *command, char *args, int from_tty)
 {
@@ -145,30 +147,51 @@ cmdpy_function (struct cmd_list_element *command, char *args, int from_tty)
 				       ttyobj, NULL);
   Py_DECREF (argobj);
   Py_DECREF (ttyobj);
+
   if (! result)
     {
       PyObject *ptype, *pvalue, *ptraceback;
+      char *msg;
 
       PyErr_Fetch (&ptype, &pvalue, &ptraceback);
 
-      if (pvalue && PyString_Check (pvalue))
-	{
-	  /* Make a temporary copy of the string data.  */
-	  char *s = PyString_AsString (pvalue);
-	  char *copy = alloca (strlen (s) + 1);
+      /* Try to fetch an error message contained within ptype, pvalue.
+	 When fetching the error message we need to make our own copy,
+	 we no longer own ptype, pvalue after the call to PyErr_Restore.  */
 
-	  strcpy (copy, s);
+      msg = gdbpy_exception_to_string (ptype, pvalue);
+      make_cleanup (xfree, msg);
+
+      if (msg == NULL)
+	{
+	  /* An error occurred computing the string representation of the
+	     error message.  This is rare, but we should inform the user.  */
+	  printf_filtered (_("An error occurred in a Python command\n"
+			     "and then another occurred computing the error message.\n"));
+	  gdbpy_print_stack ();
+	}
+
+      /* Don't print the stack for gdb.GdbError exceptions.
+	 It is generally used to flag user errors.
+
+	 We also don't want to print "Error occurred in Python command"
+	 for user errors.  However, a missing message for gdb.GdbError
+	 exceptions is arguably a bug, so we flag it as such.  */
+
+      if (! PyErr_GivenExceptionMatches (ptype, gdbpy_gdberror_exc)
+	  || msg == NULL || *msg == '\0')
+	{
 	  PyErr_Restore (ptype, pvalue, ptraceback);
 	  gdbpy_print_stack ();
-	  error (_("Error occurred in Python command: %s"), copy);
+	  if (msg != NULL && *msg != '\0')
+	    error (_("Error occurred in Python command: %s"), msg);
+	  else
+	    error (_("Error occurred in Python command."));
 	}
       else
-	{
-	  PyErr_Restore (ptype, pvalue, ptraceback);
-	  gdbpy_print_stack ();
-	  error (_("Error occurred in Python command."));
-	}
+	error ("%s", msg);
     }
+
   Py_DECREF (result);
   do_cleanups (cleanup);
 }
@@ -589,3 +612,55 @@ static PyTypeObject cmdpy_object_type =
   0,				  /* tp_alloc */
   PyType_GenericNew		  /* tp_new */
 };
+
+
+
+/* Utility to build a buildargv-like result from ARGS.
+   This intentionally parses arguments the way libiberty/argv.c:buildargv
+   does.  It splits up arguments in a reasonable way, and we want a standard
+   way of parsing arguments.  Several gdb commands use buildargv to parse their
+   arguments.  Plus we want to be able to write compatible python
+   implementations of gdb commands.  */
+
+PyObject *
+gdbpy_string_to_argv (PyObject *self, PyObject *args)
+{
+  PyObject *py_argv;
+  char *input;
+
+  if (!PyArg_ParseTuple (args, "s", &input))
+    return NULL;
+
+  py_argv = PyList_New (0);
+
+  /* buildargv uses NULL to represent an empty argument list, but we can't use
+     that in Python.  Instead, if ARGS is "" then return an empty list.
+     This undoes the NULL -> "" conversion that cmdpy_function does.  */
+
+  if (*input != '\0')
+    {
+      char **c_argv = gdb_buildargv (input);
+      int i;
+
+      for (i = 0; c_argv[i] != NULL; ++i)
+	{
+	  PyObject *argp = PyString_FromString (c_argv[i]);
+
+	  if (argp == NULL
+	      || PyList_Append (py_argv, argp) < 0)
+	    {
+	      if (argp != NULL)
+		{
+		  Py_DECREF (argp);
+		}
+	      Py_DECREF (py_argv);
+	      freeargv (c_argv);
+	      return NULL;
+	    }
+	}
+
+      freeargv (c_argv);
+    }
+
+  return py_argv;
+}

gdb/python/py-utils.c

@@ -222,3 +222,53 @@ gdbpy_is_string (PyObject *obj)
 {
   return PyString_Check (obj) || PyUnicode_Check (obj);
 }
+
+/* Return the string representation of OBJ, i.e., str (obj).
+   Space for the result is malloc'd, the caller must free.
+   If the result is NULL a python error occurred, the caller must clear it.  */
+
+char *
+gdbpy_obj_to_string (PyObject *obj)
+{
+  PyObject *str_obj = PyObject_Str (obj);
+
+  if (str_obj != NULL)
+    {
+      char *msg = xstrdup (PyString_AsString (str_obj));
+
+      Py_DECREF (str_obj);
+      return msg;
+    }
+
+  return NULL;
+}
+
+/* Return the string representation of the exception represented by
+   TYPE, VALUE which is assumed to have been obtained with PyErr_Fetch,
+   i.e., the error indicator is currently clear.
+   Space for the result is malloc'd, the caller must free.
+   If the result is NULL a python error occurred, the caller must clear it.  */
+
+char *
+gdbpy_exception_to_string (PyObject *ptype, PyObject *pvalue)
+{
+  PyObject *str_obj = PyObject_Str (pvalue);
+  char *str;
+
+  /* There are a few cases to consider.
+     For example:
+     pvalue is a string when PyErr_SetString is used.
+     pvalue is not a string when raise "foo" is used, instead it is None
+     and ptype is "foo".
+     So the algorithm we use is to print `str (pvalue)' if it's not
+     None, otherwise we print `str (ptype)'.
+     Using str (aka PyObject_Str) will fetch the error message from
+     gdb.GdbError ("message").  */
+
+  if (pvalue && pvalue != Py_None)
+    str = gdbpy_obj_to_string (pvalue);
+  else
+    str = gdbpy_obj_to_string (ptype);
+
+  return str;
+}

gdb/python/python-internal.h

@@ -92,6 +92,7 @@ PyObject *gdbpy_block_for_pc (PyObject *self, PyObject *args);
 PyObject *gdbpy_lookup_type (PyObject *self, PyObject *args, PyObject *kw);
 PyObject *gdbpy_create_lazy_string_object (CORE_ADDR address, long length,
 					   const char *encoding, struct type *type);
+PyObject *gdbpy_string_to_argv (PyObject *self, PyObject *args);
 PyObject *gdbpy_get_hook_function (const char *);
 PyObject *gdbpy_parameter (PyObject *self, PyObject *args);
 PyObject *gdbpy_parameter_value (enum var_types type, void *var);
@@ -179,6 +180,9 @@ PyObject *python_string_to_target_python_string (PyObject *obj);
 char *python_string_to_host_string (PyObject *obj);
 PyObject *target_string_to_unicode (const gdb_byte *str, int length);
 int gdbpy_is_string (PyObject *obj);
+char *gdbpy_obj_to_string (PyObject *obj);
+char *gdbpy_exception_to_string (PyObject *ptype, PyObject *pvalue);
+
 int gdbpy_is_lazy_string (PyObject *result);
 gdb_byte *gdbpy_extract_lazy_string (PyObject *string,
 				     struct type **str_type, 
@@ -197,4 +201,6 @@ extern PyObject *gdbpy_children_cst;
 extern PyObject *gdbpy_to_string_cst;
 extern PyObject *gdbpy_display_hint_cst;
 
+extern PyObject *gdbpy_gdberror_exc;
+
 #endif /* GDB_PYTHON_INTERNAL_H */

gdb/python/python.c

@@ -57,6 +57,8 @@ PyObject *gdbpy_children_cst;
 PyObject *gdbpy_display_hint_cst;
 PyObject *gdbpy_doc_cst;
 
+/* The GdbError exception.  */
+PyObject *gdbpy_gdberror_exc;
 
 /* Architecture and language to be used in callbacks from
    the Python interpreter.  */
@@ -655,6 +657,9 @@ Enables or disables printing of Python stack traces."),
   PyModule_AddStringConstant (gdb_module, "HOST_CONFIG", (char*) host_name);
   PyModule_AddStringConstant (gdb_module, "TARGET_CONFIG", (char*) target_name);
 
+  gdbpy_gdberror_exc = PyErr_NewException ("gdb.GdbError", NULL, NULL);
+  PyModule_AddObject (gdb_module, "GdbError", gdbpy_gdberror_exc);
+
   gdbpy_initialize_auto_load ();
   gdbpy_initialize_values ();
   gdbpy_initialize_frames ();
@@ -771,6 +776,12 @@ Return the name of the current target charset." },
     "target_wide_charset () -> string.\n\
 Return the name of the current target wide charset." },
 
+  { "string_to_argv", gdbpy_string_to_argv, METH_VARARGS,
+    "string_to_argv (String) -> Array.\n\
+Parse String and return an argv-like array.\n\
+Arguments are separate by spaces and may be quoted."
+  },
+
   { "write", gdbpy_write, METH_VARARGS,
     "Write a string using gdb's filtered stream." },
   { "flush", gdbpy_flush, METH_NOARGS,