sigvec(3UCB) SunOS/BSD Compatibility Library Functions sigvec(3UCB)
sigvec - software signal facilities
/usr/ucb/cc [ flag ... ] file...
int sigvec(sig, nvec, ovec)
struct sigvec *nvec, *ovec;
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 han-
dler 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 to be 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() or sigsetmask() call, or when a signal is deliv-
ered to the process.
A process may also specify a set of flags for a signal that affect the delivery of that signal.
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 cur-
rently blocked by the process then it is delivered to the process. When a signal is delivered, the current state of the process is saved,
a new signal mask is calculated (as described below), and the signal handler is invoked. The call to the handler is arranged so that if the
signal handling routine returns normally the process will resume execution in the context from before the signal's delivery. If the
process wishes to resume 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 sig-
block() or sigsetmask() call is made). This mask is formed by taking the current signal mask, adding the signal to be delivered, and ORing
in the signal mask associated with the handler to be invoked.
The action to be taken when the signal is delivered is specified by a sigvec() structure, which includes the following members:
void (*sv_handler)(); /* signal handler */
int sv_mask; /* signal mask to apply */
int sv_flags; /* see signal options */
#define SV_ONSTACK /* take signal on signal stack */
#define SV_INTERRUPT /* do not restart system on signal
#define SV_RESETHAND /* reset handler to SIG_DFL when
If the SV_ONSTACK bit is set in the flags for that signal, the system will deliver the signal to the process on the signal stack specified
with sigstack(3UCB) rather than delivering the signal on the current stack.
If nvec is not a NULL pointer, sigvec() assigns the handler specified by sv_handler(), the mask specified by sv_mask(), and the flags spec-
ified by sv_flags() to the specified signal. If nvec is a NULL pointer, sigvec() does not change the handler, mask, or flags for the spec-
The mask specified in nvec is not allowed to block SIGKILL, SIGSTOP, or SIGCONT. The system enforces this restriction silently.
If ovec is not a NULL pointer, the handler, mask, and flags in effect for the signal before the call to sigvec() are returned to the user.
A call to sigvec() with nvec a NULL pointer and ovec not a NULL pointer can be used to determine the handling information currently in
effect for a signal without changing that information.
The following is a list of all signals with names as in the include file <signal.h>:
SIGILL* illegal instruction
SIGTRAP* trace trap
SIGABRT* abort (generated by abort(3C) routine)
SIGEMT* emulator trap
SIGFPE* arithmetic exception
SIGKILL kill (cannot be caught, blocked, or ignored)
SIGBUS* bus error
SIGSEGV* segmentation violation
SIGSYS* bad argument to function
SIGPIPE write on a pipe or other socket with no one to read it
SIGALRM alarm clock
SIGTERM software termination signal
SIGURG* urgent condition present on socket
SIGSTOP** stop (cannot be caught, blocked, or ignored)
SIGTSTP** stop signal generated from keyboard
SIGCONT* continue after stop (cannot be blocked)
SIGCHLD* child status has changed
SIGTTIN** background read attempted from control terminal
SIGTTOU** background write attempted to control terminal
SIGIO* I/O is possible on a descriptor (see fcntl(2))
SIGXCPU cpu time limit exceeded (see getrlimit(2))
SIGXFSZ file size limit exceeded (see getrlimit(2))
SIGVTALRM virtual time alarm; see setitimer() on getitimer(2)
SIGPROF profiling timer alarm; see setitimer() on getitimer(2)
SIGWINCH* window changed (see termio(7I))
SIGLOST resource lost (see lockd(1M))
SIGUSR1 user-defined signal 1
SIGUSR2 user-defined signal 2
The starred signals in the list above cause a core image if not caught or ignored.
Once a signal handler is installed, it remains installed until another sigvec() call is made, or an execve(2) is performed, unless the
SV_RESETHAND bit is set in the flags for that signal. In that case, the value of the handler for the caught signal will be set to SIG_DFL
before entering the signal-catching function, unless the signal is SIGILL, SIGPWR, or SIGTRAP. Also, if this bit is set, the bit for that
signal in the signal mask will not be set; unless the signal mask associated with that signal blocks that signal, further occurrences of
that signal will not be blocked. The SV_RESETHAND flag is not available in 4.2BSD, hence it should not be used if backward compatibility is
The default action for a signal may be reinstated by setting the signal's handler to SIG_DFL; this default is termination except for sig-
nals marked with * or **. Signals marked with * are discarded if the action is SIG_DFL; signals marked with ** cause the process to stop.
If the process is terminated, a "core image" will be made in the current working directory of the receiving process if the signal is one
for which an asterisk appears in the above list (see core(4)).
If the handler for that signal is SIG_IGN, the signal is subsequently ignored, and pending instances of the signal are discarded.
If a caught signal occurs during certain functions, 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 the flags for that signal. The SV_INTERRUPT flag is not available in 4.2BSD, hence it
should not be used if backward compatibility is needed. The affected functions are read(2) or write(2) on a slow device (such as a terminal
or pipe or other socket, but not a file) and during a wait(3C).
After a fork(2) or vfork(2) the child inherits all signals, the signal mask, the signal stack, and the restart/interrupt and reset-signal-
The execve(2) call resets all caught signals to default action and resets all signals to be caught on the user stack. Ignored signals
remain ignored; the signal mask remains the same; signals that interrupt functions continue to do so.
The accuracy of addr is machine dependent. For example, certain machines may supply an address that is on the same page as the address that
caused the fault. If an appropriate addr cannot be computed it will be set to SIG_NOADDR.
A 0 value indicates that the call succeeded. A -1 return value indicates that an error occurred and errno is set to indicate the reason.
sigvec() will fail and no new signal handler will be installed if one of the following occurs:
EFAULT Either nvec or ovec is not a NULL pointer and points to memory that is not a valid part of the process address space.
EINVAL sig is not a valid signal number, or, SIGKILL, or SIGSTOP.
cc(1B), Intro(2), exec(2), fcntl(2), fork(2), getitimer(2), getrlimit(2), ioctl(2), kill(2), read(2), umask(2), vfork(2), write(2),
ptrace(3C), setjmp(3C) sigblock(3UCB), signal(3C), signal(3UCB), sigstack(3UCB), wait(3C), wait(3UCB), core(4), streamio(7I), termio(7I)
Use of these interfaces should be restricted to only applications written on BSD platforms. Use of these interfaces with any of the system
libraries or in multi-thread applications is unsupported.
SIGPOLL is a synonym for SIGIO. A SIGIO will be issued when a file descriptor corresponding to a STREAMS (see Intro(2)) file has a
"selectable" event pending. Unless that descriptor has been put into asynchronous mode (see fcntl(2)), a process may specifically request
that this signal be sent using the I_SETSIG ioctl(2) call (see streamio(7I)). Otherwise, the process will never receive SIGPOLLs0.
The handler routine can be declared:
void handler(int sig, int code, struct sigcontext *scp,
Here sig is the signal number; code is a parameter of certain signals that provides additional detail; scp is a pointer to the sigcontext
structure (defined in signal.h), used to restore the context from before the signal; and addr is additional address information.
The signals SIGKILL, SIGSTOP, and SIGCONT cannot be ignored.
SunOS 5.11 30 Oct 2007 sigvec(3UCB)