sigvec(3) UNIX System V(BSD Compatibility Package) 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
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 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.
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sigvec(3) UNIX System V(BSD Compatibility Package) sigvec(3)
The action to be taken when the signal is delivered is specified by a
sigvec structure, which includes the following members:
void (*svhandler)(); /* signal handler */
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
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sigvec(3) UNIX System V(BSD Compatibility Package) sigvec(3)
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
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 compatibility is needed.
The default action for a signal may be reinstated 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.
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sigvec(3) UNIX System V(BSD Compatibility Package) sigvec(3)
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
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 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.
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), sigstack(2),
umask(2), wait(2), write(2), setjmp(3) in the Programmer's Reference
Manual
streamio(7), termio(7) in the System Administrator's Reference 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 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.
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