sigvec(3) C LIBRARY FUNCTIONS sigvec(3)
NAME
sigvec - software signal facilities
SYNOPSIS
cc [ flag... ] file ... -lucb
#include <signal.h>
int sigvec(sig, vec, ovec)
int sig;
struct sigvec *vec, *ovec;
DESCRIPTION
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 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(3) or sigsetmask(3) call, or when a signal
is delivered 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 currently 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 pre-
vious context itself. When a signal is delivered to a pro-
cess a new signal mask is installed for the duration of the
process' signal handler (or until a sigblock 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 follow-
ing members:
void (*svhandler)(); /* signal handler */
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sigvec(3) C LIBRARY FUNCTIONS sigvec(3)
int svmask; /* signal mask to apply */
int svflags; /* see signal options */
#define SVONSTACK /* take signal on signal stack */
#define SVINTERRUPT /* do not restart system on signal return */
#define SVRESETHAND /* reset handler to SIGDFL when signal taken */
If the SVONSTACK 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(2), rather than
delivering the signal on the current stack. If vec is not a
NULL pointer, sigvec assigns the handler specified by
svhandler, the mask specified by svmask, and the flags
specified by svflags to the specified signal. If vec is a
NULL pointer, sigvec does not change the handler, mask, or
flags for the specified signal. The mask specified in vec
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 vec 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 /usr/include/signal.h:
SIGHUP hangup
SIGINT interrupt
SIGQUIT * quit
SIGILL * illegal instruction
SIGTRAP * trace trap
SIGABRT * abort (generated by abort(3) 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 system call
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 setrlimit(2)]
SIGXFSZ file size limit exceeded [see setrlimit(2)]
SIGVTALRM virtual time alarm [see setitimer(2)]
SIGPROF profiling timer alarm [see setitimer(2)]
SIGWINCH @ window changed [see termio(4)]
SIGUSR1 user-defined signal 1
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sigvec(3) C LIBRARY FUNCTIONS sigvec(3)
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 SVRESETHAND 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 SIGDFL
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 SVRESETHAND flag is not available in
4.2BSD, hence it should not be used if backward compatibil-
ity is needed. The default action for a signal may be rein-
stated by setting the signal's handler to SIGDFL; this
default is termination except for signals marked with @ or
†. Signals marked with @ are discarded if the action is
SIGDFL; 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
SIGIGN, the signal is subsequently ignored, and pending
instances of the signal are discarded. If a caught signal
occurs during certain system calls, the call is normally
restarted. The call can be forced to terminate prematurely
with an EINTR error return by setting the SVINTERRUPT bit
in the flags for that signal. The SVINTERRUPT flag is not
available in 4.2BSD, hence it should not be used if backward
compatibility is needed. The affected system calls 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(2).
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-handler flags. 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 system calls 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 can-
not be computed it will be set to SIGNOADDR.
RETURN VALUE
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.
ERRORS
sigvec will fail and no new signal handler will be installed
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sigvec(3) C LIBRARY FUNCTIONS sigvec(3)
if one of the following occurs:
EFAULT Either vec 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, SIG-
KILL, or SIGSTOP.
SEE ALSO
signal(3), sigpause(3), sigsetmask(3), wait(3). exec(2),
fcntl(2), fork(2), getrlimit(2), getitimer(2), ioctl(2),
kill(2), ptrace(2), read(2), sigblock(2), signal(2), sig-
stack(2), umask(2), wait(2), write(2), setjmp(3) in the
Programmer's Reference Manual.
streamio(7), termio(7) in the System Administrator's Refer-
ence Manual.
NOTES
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 must specifically request that this
signal be sent using the ISETSIG ioctl call [see
streamio(4)]. Otherwise, the process will never receive
SIGPOLL. The handler routine can be declared:
void handler(sig, code, scp, addr)
int sig, code;
struct sigcontext *scp;
char *addr;
Here sig is the signal number; code is a parameter of cer-
tain 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.
Last change: BSD Compatibility Package 4