RTEMS C User's Guide
When one of the critical system events occur, the user extensions are invoked in either "forward" or "reverse" order. Forward order indicates that the static extension set is invoked followed by the dynamic extension sets in the order in which they were created. Reverse order means that the dynamic extension sets are invoked in the opposite of the order in which they were created followed by the static extension set. By invoking the extension sets in this order, extensions can be built upon one another. At the following system events, the extensions are invoked in forward order:
At the following system events, the extensions are invoked in reverse order:
At these system events, the extensions are invoked in reverse order to insure that if an extension set is built upon another, the more complicated extension is invoked before the extension set it is built upon. For example, by invoking the static extension set last it is known that the "system" fatal error extension will be the last fatal error extension executed. Another example is use of the task delete extension by the Standard C Library. Extension sets which are installed after the Standard C Library will operate correctly even if they utilize the C Library because the C Library's TASK_DELETE extension is invoked after that of the other extensions.
RTEMS C User's Guide
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