It is… not? It simply invokes the unwinder / exception handler, like _Unwind_RaiseException. For normal exceptions, no signals are involved. You can get an idea of what is executed at http://stffrdhrn.github.io/software/toolchain/openrisc/2020/....

Are you referring to interrupts by any chance? The OS has nothing whatsoever to do with C++ exceptions in user-mode code.

Usermode exception handling performs no system calls. Perhaps you're thinking of user handling of system exceptions on Windows, which are pretty much unrelated to C++ exceptions?

Is that incurred for user-initiated exceptions (not traps or Windows "SEH")? In which implementations?