_Unwind_ForcedUnwind raises an exception for forced unwinding, passing along the given exception object, which should have its exception_class and exception_cleanup fields set. The exception object has been allocated by the language-specific runtime, and has a language-specific format, except that it must contain an _Unwind_Exception struct.
Forced unwinding is a single-phase process. stop and stop_parameter control the termination of the unwind process instead of the usual personality routine query. stop is called for each unwind frame, with the parameteres described for the usual personality routine below, plus an additional stop_parameter.
When stop identifies the destination frame, it transfers control to the user code as appropriate without returning, normally after calling _Unwind_DeleteException. If not, then it should return an _Unwind_Reason_Code value.
If stop returns any reason code other than _URC_NO_REASON, then the stack state is indeterminate from the point of view of the caller of _Unwind_ForcedUnwind. Rather than attempt to return, therefore, the unwind library should use the exception_cleanup entry in the exception, and then call abort.
This is not the destination from. The unwind runtime will call frame's personality routine with the _UA_FORCE_UNWIND and _UA_CLEANUP_PHASE flag set in actions, and then unwind to the next frame and call the stop function again.
In order to allow _Unwind_ForcedUnwind to perform special processing when it reaches the end of the stack, the unwind runtime will call it after the last frame is rejected, with a NULL stack pointer in the context, and the stop function must catch this condition. It may return this code if it cannot handle end-of-stack.
The stop function may return this code for other fatal conditions like stack corruption.