SIGNAL(II) 8/5/73 SIGNAL(II) NAME signal - catch or ignore signals SYNOPSIS (signal = 48.) sys signal; sig; label (old value in r0) signal(sig, func) int (*func)(); DESCRIPTION When the signal defined by sig is sent to the current process, it is to be treated according to label (resp. func.) The following is the list of signals: 1 hangup 2 interrupt 3* quit 4* illegal instruction 5* trace trap 6* IOT instruction 7* EMT instruction 8* floating point exception 9 kill (cannot be caught or ignored) 10* bus error 11* segmentation violation 12* bad argument to sys call If label is 0, the default system action applies to the signal. This is processes termination with or without a core dump. If label is odd, the signal is ignored. Any other even label specifies an address in the process where an interrupt is simulated. An RTI instruction will return from the interrupt. As a signal is caught, it is reset to 0. Thus if it is desired to catch every such signal, the catching routine must issue another signal call. In C, if func is 0 or 1, the action is as described above. If func is even, it is assumed to be the address of a function entry point. When the signal occurs, the function will be called. A return from the function will simulate the RTI. The starred signals in the list above cause core images if not caught and not ignored. In assembly language, the old value of the signal is returned in r0. In C, that value is retruned. After a fork, the child inherits all signals. The exec call resets all caught signals to default action. SEE ALSO kill (I), kill (II) DIAGNOSTICS The error bit (c-bit) is set if the given signal is out of range. In C, a -1 indicates an error; 0 indicates success.