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

     sigvec -- software signal facilities

     Standard C Library (libc, -lc)

     #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 deliv-ered, delivered,
     ered, 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 invoca-tion invocation
     tion blocked, but other signals may yet occur.  A global signal mask defines the set of signals cur-rently currently
     rently 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 process.

     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(2) or sigsetmask(2) call is made).  This mask is formed by taking
     the current 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 specified 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, specified with
     sigaltstack(2).  If ovec is non-zero, the previous handling information for the signal is returned to
     the user.

     The following is a list of all signals with names as in the include file <signal.h>:

     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 socket
     SIGSTOP         stop process            stop (cannot be caught or ignored)
     SIGTSTP         stop process            stop signal generated from keyboard
     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 setrlimit(2))
     SIGXFSZ         terminate process       file size limit exceeded (see setrlimit(2))
     SIGVTALRM       terminate process       virtual time alarm (see setitimer(2))
     SIGPROF         terminate process       profiling timer alarm (see setitimer(2))
     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 defaults are process termination, possibly with core dump; no action; stopping 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

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

     The sigvec() function returns the value 0 if successful; otherwise the value -1 is returned and the
     global variable errno is set to indicate the error.

     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

     [EINVAL]           Sig is not a valid signal number.

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

     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 constant 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.

BSD                             April 19, 1994                             BSD

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