rtems-docs/c-user/fatal_error.rst

.. comment SPDX-License-Identifier: CC-BY-SA-4.0

.. COMMENT: COPYRIGHT (c) 1988-2008.
.. COMMENT: On-Line Applications Research Corporation (OAR).
.. COMMENT: All rights reserved.

Fatal Error Manager
*******************

.. index:: fatal errors

Introduction
============

The fatal error manager processes all fatal or irrecoverable errors and other
sources of system termination (for example after ``exit()``).  The directives
provided by the fatal error manager are:

- rtems_fatal_error_occurred_ - Invoke the fatal error handler

- rtems_fatal_ - Invoke the fatal error handler with error source

- rtems_exception_frame_print_ - Print the CPU exception frame

- rtems_fatal_source_text_ - Return the falet source text

- rtems_internal_error_text_ - Return the error code text

Background
==========
.. index:: fatal error detection
.. index:: fatal error processing
.. index:: fatal error user extension

The fatal error manager is called upon detection of an irrecoverable error
condition by either RTEMS or the application software.  Fatal errors can be
detected from three sources:

- the executive (RTEMS)

- user system code

- user application code

RTEMS automatically invokes the fatal error manager upon detection of an error
it considers to be fatal.  Similarly, the user should invoke the fatal error
manager upon detection of a fatal error.

Each static or dynamic user extension set may include a fatal error handler.
The fatal error handler in the static extension set can be used to provide
access to debuggers and monitors which may be present on the target hardware.
If any user-supplied fatal error handlers are installed, the fatal error
manager will invoke them.  If no user handlers are configured or if all the
user handler return control to the fatal error manager, then the RTEMS default
fatal error handler is invoked.  If the default fatal error handler is invoked,
then the system state is marked as failed.

Although the precise behavior of the default fatal error handler is processor
specific, in general, it will disable all maskable interrupts, place the error
code in a known processor dependent place (generally either on the stack or in
a register), and halt the processor.  The precise actions of the RTEMS fatal
error are discussed in the Default Fatal Error Processing chapter of the
Applications Supplement document for a specific target processor.

Operations
==========

.. _Announcing a Fatal Error:

Announcing a Fatal Error
------------------------
.. index:: _Internal_errors_What_happened

The ``rtems_fatal_error_occurred`` directive is invoked when a fatal error is
detected.  Before invoking any user-supplied fatal error handlers or the RTEMS
fatal error handler, the ``rtems_fatal_error_occurred`` directive stores useful
information in the variable ``_Internal_errors_What_happened``.  This structure
contains three pieces of information:

- the source of the error (API or executive core),

- whether the error was generated internally by the executive, and a

- a numeric code to indicate the error type.

The error type indicator is dependent on the source of the error and whether or
not the error was internally generated by the executive.  If the error was
generated from an API, then the error code will be of that API's error or
status codes.  The status codes for the RTEMS API are in
cpukit/rtems/include/rtems/rtems/status.h.  Those for the POSIX API can be
found in <errno.h>.

The ``rtems_fatal_error_occurred`` directive is responsible for invoking an
optional user-supplied fatal error handler and/or the RTEMS fatal error
handler.  All fatal error handlers are passed an error code to describe the
error detected.

Occasionally, an application requires more sophisticated fatal error processing
such as passing control to a debugger.  For these cases, a user-supplied fatal
error handler can be specified in the RTEMS configuration table.  The User
Extension Table field fatal contains the address of the fatal error handler to
be executed when the ``rtems_fatal_error_occurred`` directive is called.  If
the field is set to NULL or if the configured fatal error handler returns to
the executive, then the default handler provided by RTEMS is executed.  This
default handler will halt execution on the processor where the error occurred.

Directives
==========

This section details the fatal error manager's directives.  A subsection is
dedicated to each of this manager's directives and describes the calling
sequence, related constants, usage, and status codes.

.. raw:: latex

   \clearpage

.. _rtems_fatal_error_occurred:

FATAL_ERROR_OCCURRED - Invoke the fatal error handler
-----------------------------------------------------
.. index:: announce fatal error
.. index:: fatal error, announce
.. index:: rtems_fatal_error_occurred

CALLING SEQUENCE:
    .. code-block:: c

        void rtems_fatal_error_occurred(
            uint32_t  the_error
        );

DIRECTIVE STATUS CODES:
    NONE

DESCRIPTION:
    This directive processes fatal errors.  If the FATAL error extension is
    defined in the configuration table, then the user-defined error extension
    is called.  If configured and the provided FATAL error extension returns,
    then the RTEMS default error handler is invoked.  This directive can be
    invoked by RTEMS or by the user's application code including initialization
    tasks, other tasks, and ISRs.

NOTES:
    This directive supports local operations only.

    Unless the user-defined error extension takes special actions such as
    restarting the calling task, this directive WILL NOT RETURN to the caller.

    The user-defined extension for this directive may wish to initiate a global
    shutdown.

.. raw:: latex

   \clearpage

.. _rtems_fatal:

FATAL - Invoke the fatal error handler with error source
--------------------------------------------------------
.. index:: announce fatal error
.. index:: fatal error, announce
.. index:: rtems_fatal

CALLING SEQUENCE:
    .. code-block:: c

        void rtems_fatal(
           rtems_fatal_source source,
           rtems_fatal_code   error
        );

DIRECTIVE STATUS CODES:
    NONE

DESCRIPTION:
    This directive invokes the internal error handler with is internal set to
    false.  See also ``rtems_fatal_error_occurred``.

.. raw:: latex

   \clearpage

.. _rtems_exception_frame_print:

EXCEPTION_FRAME_PRINT - Prints the exception frame
--------------------------------------------------
.. index:: exception frame
.. index:: rtems_exception_frame_print

CALLING SEQUENCE:
    .. code-block:: c

        void rtems_exception_frame_print(
            const rtems_exception_frame *frame
        );

DIRECTIVE STATUS CODES:
    NONE

DESCRIPTION:
    Prints the exception frame via ``printk()``.

.. raw:: latex

   \clearpage

.. _rtems_fatal_source_text:

FATAL_SOURCE_TEXT - Returns a text for a fatal source
-----------------------------------------------------
.. index:: fatal error
.. index:: rtems_fatal_source_text

CALLING SEQUENCE:
    .. code-block:: c

        const char *rtems_fatal_source_text(
            rtems_fatal_source source
        );

DIRECTIVE STATUS CODES:
    The fatal source text or "?" in case the passed fatal source is invalid.

DESCRIPTION:
    Returns a text for a fatal source.  The text for fatal source is the
    enumerator constant.

.. raw:: latex

   \clearpage

.. _rtems_internal_error_text:

INTERNAL_ERROR_TEXT - Returns a text for an internal error code
---------------------------------------------------------------
.. index:: fatal error
.. index:: rtems_internal_error_text

CALLING SEQUENCE:
    .. code-block:: c

        const char *rtems_internal_error_text(
            rtems_fatal_code error
        );

DIRECTIVE STATUS CODES:
    The error code text or "?" in case the passed error code is invalid.

DESCRIPTION:
    Returns a text for an internal error code.  The text for each internal
    error code is the enumerator constant.