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+.. SPDX-License-Identifier: CC-BY-SA-4.0
+
+.. Copyright (C) 2020 embedded brains GmbH & Co. KG
+
+.. _Migration_5_to_6:
+
+RTEMS 5 to RTEMS 6
+==================
+
+This section provides helpful information when migrating from RTEMS 5 to
+RTEMS 6.
+
+Update to GCC 10 and Later
+--------------------------
+
+The tool suite for RTEMS 6 uses at least GCC 10.  GCC 10 and later enable
+``-fno-common`` by default.  Code bases which never used this option before may
+observe now multiple definition linker errors.  For example, if global
+variables are declared and defined in header files (usually a missing
+``extern`` in the header file).
+
+No -specs bsp_specs GCC Option
+------------------------------
+
+The ``-spec bsp_specs`` GCC Option is no longer needed to build RTEMS
+applications and there is no :file:`bsp_specs` file installed.  If you use this
+option, then you get an error like this:
+
+.. code-block:: none
+
+    sparc-rtems6-gcc: fatal error: cannot read spec file 'bsp_specs': No such file or directory
+
+You can remove this GCC option from your build to fix this error.
+Alternatively, you can add an empty :file:`bsp_specs` file.
+
+Replacements for Removed APIs
+-----------------------------
+
+* The ``rtems_iterate_over_all_threads()`` directive was removed. Use
+  ``rtems_task_iterate()`` instead.
+
+* The ``rtems_get_current_processor()`` directive was removed. Use
+  ``rtems_scheduler_get_processor()`` instead.
+
+* The ``rtems_get_processor_count()`` directive was removed. Use
+  ``rtems_scheduler_get_processor_maximum()`` instead.
+
+* The ``boolean`` type was removed. Use ``bool`` instead.
+
+* The ``single_precision`` type was removed. Use ``float`` instead.
+
+* The ``double_precision`` type was removed. Use ``double`` instead.
+
+* The ``proc_ptr`` type was removed. Use a proper function pointer type.
+
+* The ``rtems_context`` type was removed.  If you need this type in your
+  applications, please ask on the :r:list:`devel`.
+
+* The ``rtems_context_fp`` type was removed.  If you need this type in your
+  applications, please ask on the :r:list:`devel`.
+
+* The ``rtems_extension`` type was removed.  Use ``void`` instead.
+
+* The ``rtems_io_lookup_name()`` directive was removed. Use ``stat()`` instead.
+
+* The ``region_information_block`` type was removed. Use
+  ``Heap_Information_block`` instead.
+
+* The ``rtems_thread_cpu_usage_t`` type was removed. Use ``struct timespec``
+  instead.
+
+* The ``rtems_rate_monotonic_period_time_t`` type was removed. Use ``struct
+  timespec`` instead.
+
+* The ``_Copyright_Notice`` constant was removed from the API. Use
+  ``rtems_get_copyright_notice()`` instead.
+
+* The ``_RTEMS_version`` constant was removed from the API. Use
+  ``rtems_get_version_string()`` instead.
+
+* The ``RTEMS_MAXIMUM_NAME_LENGTH`` define was removed. Use
+  ``sizeof( rtems_name )`` instead.
+
+* The ``<rtems/system.h>`` header file was removed. Include ``<rtems.h>``
+  instead.