Reading modules/objfmts/coff/win64-except.c I could help noticing UNW_FLAG_CHAININFO defintion assigning value of 3. The correct value is 4, not 3. Well, it's not used anywhere for the moment, so it's not really a problem now. But it will naturally cause grief when you attempt to use it, so it makes sense to fix it.
As for what can go wrong. Note UNW_FLAG_[EU]HANDLER values. It's actually possible to combine these two to 2|1=3 and have same subroutine serve as exception and "termination" handler. The latter is one corresponding to __finally in __try/__finally construct in visual c. With value or 3 system will call handler first as exception handler and if it returns "not handled, keep looking" return code, the system will call it second time as "termination" handler. A.
