SIGVEC(2)SIGVEC(2)NAME
sigvec - software signal facilities
SYNOPSIS
#include <signal.h>
struct sigvec {
int (*sv_handler)();
int sv_mask;
int sv_flags;
};
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 occurence 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 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(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 or
sigsetmask 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 sigstack(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>:
SIGHUP 1 hangup
SIGINT 2 interrupt
SIGQUIT 3* quit
SIGILL 4* illegal instruction
SIGTRAP 5* trace trap
SIGIOT 6* IOT instruction
SIGEMT 7* EMT instruction
SIGFPE 8* floating point exception
SIGKILL 9 kill (cannot be caught, blocked, or ignored)
SIGBUS 10* bus error
SIGSEGV 11* segmentation violation
SIGSYS 12* bad argument to system call
SIGPIPE 13 write on a pipe with no one to read it
SIGALRM 14 alarm clock
SIGTERM 15 software termination signal
SIGURG 16@ urgent condition present on socket
SIGSTOP 17|+'stop (cannot be caught, blocked, or ignored)
SIGTSTP 18|+'stop signal generated from keyboard
SIGCONT 19@ continue after stop (cannot be blocked)
SIGCHLD 20@ child status has changed
SIGTTIN 21|+'background read attempted from control terminal
SIGTTOU 22|+'background write attempted to control terminal
SIGIO 23@ i/o is possible on a descriptor (see fcntl(2))
SIGXCPU 24 cpu time limit exceeded (see setrlimit(2))
SIGXFSZ 25 file size limit exceeded (see setrlimit(2))
SIGVTALRM 26 virtual time alarm (see setitimer(2))
SIGPROF 27 profiling timer alarm (see setitimer(2))
SIGWINCH 28@ window size change
SIGUSR1 30 user defined signal 1
SIGUSR2 31 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. The default action
for a signal may be reinstated by setting sv_handler to SIG_DFL; this
default is termination (with a core image for starred signals) except
for signals marked with @ or |+'. Signals marked with @ are discarded
if the action is SIG_DFL; signals marked with |+' cause the process to
stop. If sv_handler 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 sv_flags.
The affected system calls are read(2) or write(2) on a slow device
(such as a terminal; 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 flags.
Execve(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.
NOTES
The mask specified in vec is not allowed to block SIGKILL, SIGSTOP, or
SIGCONT. This is done silently by the system.
The SV_INTERRUPT flag is not available in 4.2BSD, hence it should not
be used if backward compatibility is needed.
RETURN VALUE
A 0 value indicated that the call succeeded. A -1 return value
indicates an error occurred and errno is set to indicated 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 points to memory that is not a valid
part of the process address space.
[EINVAL] Sig is not a valid signal number.
[EINVAL] An attempt is made to ignore or supply a handler for
SIGKILL or SIGSTOP.
[EINVAL] An attempt is made to ignore SIGCONT (by default SIGCONT
is ignored).
SEE ALSOkill(1), ptrace(2), kill(2), sigblock(2), sigsetmask(2), sigpause(2),
sigstack(2), sigvec(2), setjmp(3), siginterrupt(3), tty(4)4th Berkeley Distribution January 8, 1986 SIGVEC(2)