..
  Copyright 1988-2022 Free Software Foundation, Inc.
  This is part of the GCC manual.
  For copying conditions, see the copyright.rst file.

.. _rx-function-attributes:

RX Function Attributes
^^^^^^^^^^^^^^^^^^^^^^

These function attributes are supported by the RX back end:

.. index:: fast_interrupt function attribute, RX

.. rx-fn-attr:: fast_interrupt

  Use this attribute on the RX port to indicate that the specified
  function is a fast interrupt handler.  This is just like the
  :rx-fn-attr:`interrupt` attribute, except that ``freit`` is used to return
  instead of ``reit``.

.. index:: interrupt function attribute, RX

.. rx-fn-attr:: interrupt

  Use this attribute to indicate
  that the specified function is an interrupt handler.  The compiler generates
  function entry and exit sequences suitable for use in an interrupt handler
  when this attribute is present.

  On RX and RL78 targets, you may specify one or more vector numbers as arguments
  to the attribute, as well as naming an alternate table name.
  Parameters are handled sequentially, so one handler can be assigned to
  multiple entries in multiple tables.  One may also pass the magic
  string ``"$default"`` which causes the function to be used for any
  unfilled slots in the current table.

  This example shows a simple assignment of a function to one vector in
  the default table (note that preprocessor macros may be used for
  chip-specific symbolic vector names):

  .. code-block:: c++

    void __attribute__ ((interrupt (5))) txd1_handler ();

  This example assigns a function to two slots in the default table
  (using preprocessor macros defined elsewhere) and makes it the default
  for the ``dct`` table:

  .. code-block:: c++

    void __attribute__ ((interrupt (RXD1_VECT,RXD2_VECT,"dct","$default")))
    	txd1_handler ();

.. index:: naked function attribute, RX

.. rx-fn-attr:: naked

  This attribute allows the compiler to construct the
  requisite function declaration, while allowing the body of the
  function to be assembly code. The specified function will not have
  prologue/epilogue sequences generated by the compiler. Only basic
  ``asm`` statements can safely be included in naked functions
  (see :ref:`basic-asm`). While using extended ``asm`` or a mixture of
  basic ``asm`` and C code may appear to work, they cannot be
  depended upon to work reliably and are not supported.

.. index:: vector function attribute, RX

.. rx-fn-attr:: vector

  This RX attribute is similar to the :rx-fn-attr:`interrupt` attribute, including its
  parameters, but does not make the function an interrupt-handler type
  function (i.e. it retains the normal C function calling ABI).  See the
  :rx-fn-attr:`interrupt` attribute for a description of its arguments.