Non-existent syscalls map to nosys, which sets u_error
to 100 ... which
causes the process to be sent a signal SIGSYS.
Oh, right, I'd forgotten that.
So, getting back to v6tar, I'll bet that if you try and use it to _read_ a TAR
file file under V6 (i.e. write files into the V6 filesystem), it will bomb out
(because of the call to utime).