RTEMS Porting Guide
With some compilation systems, it is difficult if not impossible to call a high-level language routine from assembly language. This is especially true of commercial Ada compilers and name mangling C++ ones. This variable can be optionally defined by the CPU porter and contains the address of the routine _Thread_Dispatch. This can make it easier to invoke that routine at the end of the interrupt sequence (if a dispatch is necessary).
void (*_CPU_Thread_dispatch_pointer)();
RTEMS Porting Guide
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