sigvec(3BSD) (BSD System Compatibility) sigvec(3BSD)
NAME
sigvec - (BSD) software signal facilities
SYNOPSIS
/usr/ucb/cc [flag . . . ] file . . .
#include <signal.h>
int sigvec(int sig, struct sigvec *vec, struct sigvec *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(3BSD) or sigsetmask(3BSD) 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 previous context
itself.
Copyright 1994 Novell, Inc. Page 1
sigvec(3BSD) (BSD System Compatibility) sigvec(3BSD)
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 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 return */
#define SV_RESETHAND /* reset handler to SIG_DFL when signal taken */
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(3BSD), rather than delivering
the signal on the current stack.
If vec is not a NULL pointer, sigvec assigns the handler
specified by sv_handler, the mask specified by sv_mask, and
the flags specified by sv_flags 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:
Copyright 1994 Novell, Inc. Page 2
sigvec(3BSD) (BSD System Compatibility) sigvec(3BSD)
SIGHUP hangup
SIGINT interrupt
SIGQUIT * quit
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 system call
SIGPIPE write on a pipe or other socket with no one to read it
SIGALRM alarm clock
SIGTERM software termination signal
SIGURG o urgent condition present on socket
SIGSTOP - stop (cannot be caught, blocked, or ignored)
SIGTSTP - stop signal generated from keyboard
SIGCONT o continue after stop (cannot be blocked)
SIGCHLD o child status has changed
SIGTTIN - background read attempted from control terminal
SIGTTOU - background write attempted to control terminal
SIGIO o I/O is possible on a descriptor [see fcntl(2)]
SIGPWR o power fail/restart
SIGXCPU cpu time limit exceeded [see getrlimit(2)]
SIGXFSZ file size limit exceeded [see getrlimit(2)]
SIGVTALRM virtual time alarm [see getitimer(3C)]
SIGPROF profiling timer alarm [see getitimer(3C)]
SIGWINCH o window changed [see termio(7)]
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 [see exec(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
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sigvec(3BSD) (BSD System Compatibility) sigvec(3BSD)
not be used if backward compatibility is needed.
The default action for a signal may be reinstated by setting
the signal's handler to SIG_DFL; this default is termination
except for signals marked with o or -. Signals marked with o
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 system calls, 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
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 call [see exec(2)] 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 cannot be computed it will be set to SIG_NOADDR.
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.
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sigvec(3BSD) (BSD System Compatibility) sigvec(3BSD)
ERRORS
sigvec will fail and no new signal handler will be installed
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, SIGKILL,
or SIGSTOP.
REFERENCES
exec(2), fcntl(2), fork(2), getitimer(3C), getrlimit(2),
ioctl(2), kill(2), ptrace(2), read(2), setjmp(3BSD),
sigblock(3BSD), signal(2), signal(3BSD), sigpause(3BSD),
sigsetmask(3BSD), sigstack(3BSD), streamio(7), termio(7),
umask(2), wait(2), wait(3BSD), write(2)
NOTICES
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
I_SETSIG ioctl call [see streamio(7)]. 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 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 and SIGSTOP cannot be ignored.
Copyright 1994 Novell, Inc. Page 5