NAME

sigvec − software signal facilities

USAGE

#include <signal.h>

struct sigvec {
int(*sv_handler)();
intsv_mask;
intsv_onstack;
};

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, 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 alsospecify a default action the system takes 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 zero).  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, the process will normally resume execution in the state it was in 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 including, with a logical or, 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 sv_onstack is 1, 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>:

SIGHUP1hang-up
SIGINT2interrupt
SIGQUIT3quit
SIGILL4illegal instruction
SIGTRAP5trace trap
SIGIOT6IOT instruction
SIGEMT7EMT instruction
SIGFPE8floating-point exception
SIGKILL9kill (cannot be caught, blocked, or ignored)
SIGBUS10bus error
SIGSEGV11segmentation violation
SIGSYS12*bad argument to system call
SIGPIPE13write on a pipe with no one to read it
SIGALRM14alarm clock
SIGTERM15software termination signal
SIGUSR116user-defined signal 1
SIGUSR217user-defined signal 2
SIGCLD18death of a child
SIGPWR19power-fail restart
SIGSTOP20stop, cannot be caught, held, or ignored
SIGTSTP21stop signal generated from keyboard
SIGCONT22continue after stop
SIGCHLD23child status has changed
SIGTTIN24background read attempted from control terminal
SIGTTOU25background write attempted to control terminal
SIGIO  26I/O is possible on a descriptor
SIGTINT26input record is available at control terminal
SIGXCPU27cpu time limit exceeded
SIGXFSZ28file size limit exceeded
SIGVTALRM29virtual time alarm
SIGPROF30profiling timer alarm
SIGURG31urgent condition present on socket

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 a bullet () or a dagger ().  Signals marked with a bullet are discarded if the action is SIG_DFL; signals marked with a dagger 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 and causes the call to terminate prematurely, the call is automatically restarted.  This is especially likely to occur during a read 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, and the signal stack. 

Execve(2) resets all caught signals to default action; ignored signals remain ignored; the signal mask remains the same; and the signal stack state is reset. 

NOTES

The system does not allow the mask specified in vec to block SIGKILL, SIGSTOP, or SIGCONT. 

The handler routine can be declared as follows:

    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 system-dependent constant.  Scp is a pointer to the sigcontext structure (defined in <signal.h>), which is used to restore the context from before the signal. 

RETURN VALUE

A zero value indicates that the call succeeded.  A −1 return value indicates that an error occurred, and errno is set to indicate the reason for failure. 

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). 

RELATED INFORMATION

kill(1), kill(2), sigblock(2), sigsetmask(2), sigpause(2) sigstack(2), sigvec(2), setjmp(3), tty(4)