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SIGVEC(2)		    BSD	System Calls Manual		     SIGVEC(2)

     sigvec -- software	signal facilities

     #include <signal.h>

     struct sigvec {
	     void     (*sv_handler)();
	     int      sv_mask;
	     int      sv_flags;

     sigvec(int	sig, struct sigvec *vec, struct	sigvec *ovec);

     This interface is made obsolete by	sigaction(2).

     The system	defines	a set of signals that may be delivered to a process.
     Signal delivery resembles the occurrence of a hardware interrupt: the
     signal is blocked from further occurrence,	the current process context is
     saved, and	a new one is built.  A process may specify a handler to	which
     a signal is delivered, or specify that a signal is	to be blocked or
     ignored.  A process may also specify that a default action	is to be taken
     by	the system when	a signal occurs.  Normally, signal handlers execute on
     the current stack of the process.	This may be changed, on	a per-handler
     basis, so that signals are	taken on a special signal stack.

     All signals have the same priority.  Signal routines execute with the
     signal that caused	their invocation blocked, but other signals may	yet
     occur.  A global signal mask defines the set of signals currently blocked
     from delivery to a	process.  The signal mask for a	process	is initialized
     from that of its parent (normally 0).  It may be changed with a
     sigblock(2) or sigsetmask(2) call,	or when	a signal is delivered to the

     When a signal condition arises for	a process, the signal is added to a
     set of signals pending for	the process.  If the signal is not currently
     blocked by	the process then it is delivered to the	process.  When a sig-
     nal is delivered, the current state of the	process	is saved, a new	signal
     mask is calculated	(as described below), and the signal handler is	in-
     voked.  The call to the handler is	arranged so that if the	signal han-
     dling routine returns normally the	process	will resume execution in the
     context from before the signal's delivery.	 If the	process	wishes to re-
     sume in a different context, then it must arrange to restore the previous
     context itself.

     When a signal is delivered	to a process a new signal mask is installed
     for the duration of the process' signal handler (or until a sigblock(2)
     or	sigsetmask(2) call is made).  This mask	is formed by taking the	cur-
     rent signal mask, adding the signal to be delivered, and or'ing in	the
     signal mask associated with the handler to	be invoked.

     Sigvec() assigns a	handler	for a specific signal.	If vec is non-zero, it
     specifies a handler routine and mask to be	used when delivering the spec-
     ified signal.  Further, if	the SV_ONSTACK bit is set in sv_flags, the
     system will deliver the signal to the process on a	signal stack, speci-
     fied with sigaltstack(2).	If ovec	is non-zero, the previous handling in-
     formation for the signal is returned to the user.

     The following is a	list of	all signals with names as in the include file

       NAME	       Default Action			   Description
     SIGHUP	     terminate process	     terminal line hangup
     SIGINT	     terminate process	     interrupt program
     SIGQUIT	     create core image	     quit program
     SIGILL	     create core image	     illegal instruction
     SIGTRAP	     create core image	     trace trap
     SIGABRT	     create core image	     abort(3) call (formerly SIGIOT)
     SIGEMT	     create core image	     emulate instruction executed
     SIGFPE	     create core image	     floating-point exception
     SIGKILL	     terminate process	     kill program
     SIGBUS	     create core image	     bus error
     SIGSEGV	     create core image	     segmentation violation
     SIGSYS	     create core image	     non-existent system call invoked
     SIGPIPE	     terminate process	     write on a	pipe with no reader
     SIGALRM	     terminate process	     real-time timer expired
     SIGTERM	     terminate process	     software termination signal
     SIGURG	     discard signal	     urgent condition present on
     SIGSTOP	     stop process	     stop (cannot be caught or
     SIGTSTP	     stop process	     stop signal generated from
     SIGCONT	     discard signal	     continue after stop
     SIGCHLD	     discard signal	     child status has changed
     SIGTTIN	     stop process	     background	read attempted from
					     control terminal
     SIGTTOU	     stop process	     background	write attempted	to
					     control terminal
     SIGIO	     discard signal	     I/O is possible on	a descriptor
					     (see fcntl(2))
     SIGXCPU	     terminate process	     cpu time limit exceeded (see
     SIGXFSZ	     terminate process	     file size limit exceeded (see
     SIGVTALRM	     terminate process	     virtual time alarm	(see
     SIGPROF	     terminate process	     profiling timer alarm (see
     SIGWINCH	     discard signal	     Window size change
     SIGINFO	     discard signal	     status request from keyboard
     SIGUSR1	     terminate process	     User defined signal 1
     SIGUSR2	     terminate process	     User defined signal 2

     Once a signal handler is installed, it remains installed until another
     sigvec() call is made, or an execve(2) is performed.  A signal-specific
     default action may	be reset by setting sv_handler to SIG_DFL.  The	de-
     faults are	process	termination, possibly with core	dump; no action; stop-
     ping the process; or continuing the process.  See the above signal	list
     for each signal's default action.	If sv_handler is SIG_IGN current and
     pending instances of the signal are ignored and discarded.

     If	a signal is caught during the system calls listed below, the call is
     normally restarted.  The call can be forced to terminate prematurely with
     an	EINTR error return by setting the SV_INTERRUPT bit in sv_flags.	 The
     affected system calls include read(2), write(2), sendto(2), recvfrom(2),
     sendmsg(2)	and recvmsg(2) on a communications channel or a	slow device
     (such as a	terminal, but not a regular file) and during a wait(2) or
     ioctl(2).	However, calls that have already committed are not restarted,
     but instead return	a partial success (for example,	a short	read count).

     After a fork(2) or	vfork(2) all signals, the signal mask, the signal
     stack, and	the restart/interrupt flags are	inherited by the child.

     Execve(2) reinstates the default action for all signals which were	caught
     and resets	all signals to be caught on the	user stack.  Ignored signals
     remain ignored; the signal	mask remains the same; signals that interrupt
     system calls continue to do so.

     The mask specified	in vec is not allowed to block SIGKILL or SIGSTOP.
     This is done silently by the system.

     The SV_INTERRUPT flag is not available in 4.2BSD, hence it	should not be
     used if backward compatibility is needed.

     A 0 value indicated that the call succeeded.  A -1	return value indicates
     an	error occurred and errno is set	to indicated the reason.

     Sigvec() will fail	and no new signal handler will be installed if one of
     the following occurs:

     [EFAULT]  Either vec or ovec points to memory that	is not a valid part of
	       the process address space.

     [EINVAL]  Sig is not a valid signal number.

     [EINVAL]  An attempt is made to ignore or supply a	handler	for SIGKILL or

     kill(1), kill(2), ptrace(2), sigaction(2),	sigaltstack(2),	sigblock(2),
     sigpause(2), sigprocmask(2), sigsetmask(2), sigsuspend(2),	setjmp(3),
     siginterrupt(3), signal(3), sigsetops(3), tty(4)

     On	the VAX-11 The handler routine can be declared:

	   void	handler(sig, code, scp)
	   int sig, code;
	   struct sigcontext *scp;

     Here sig is the signal number, into which the hardware faults and traps
     are mapped	as defined below.  Code	is a parameter that is either a	con-
     stant as given below or, for compatibility	mode faults, the code provided
     by	the hardware (Compatibility mode faults	are distinguished from the
     other SIGILL traps	by having PSL_CM set in	the psl).  Scp is a pointer to
     the sigcontext structure (defined in <signal.h>), used to restore the
     context from before the signal.

     This manual page is still confusing.

4th Berkeley Distribution	April 19, 1994	     4th Berkeley Distribution


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