Machine hang in USR mode C

I think in the common case the exception handler code itself lies in the SharedCLibrary module and is thus relatively safe

It’s true that the bulk of the code is in the module. But the entry point is a trampoline which is stored in the clients static data (i.e. application space).

https://gitlab.riscosopen.org/RiscOS/Sources/Lib/RISC_OSLib/-/blob/ae6fe48bb7285b8dfffc4aaa5bc6d4309cd9f11d/kernel/s/k_body#L813