SIGVEC(2) — Kubota Pacfic Computer Inc. (System Calls−BSD)

NAME

sigvec − software signal facilities

SYNOPSIS

#include <signal.h>

struct sigvec {
int(∗sv_handler)();
intsv_mask;
intsv_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 list gives all signals with names as they appear in the include file <signal.h>:

SIGHUP1hangup
SIGINT2interrupt (rubout)
SIGQUIT3∗quit (ASCII FS)
SIGILL4∗illegal instruction (not reset when caught)
SIGTRAP5∗trace trap (not reset when caught)
SIGIOT6∗IOT instruction (obsolete)
SIGABRT6∗used by abort, replaces SIGIOT
SIGEMT7∗EMT instruction (obsolete)
SIGFPE8∗floating point exception
SIGKILL9kill (cannot be caught, blocked, or ignored)
SIGBUS10∗bus error
SIGSEGV11∗segmentation violation
SIGSYS12∗bad argument to system call
SIGPIPE13write on a pipe with no one to read it
SIGALRM14alarm clock
SIGTERM15software termination signal
SIGUSR116 user-defined signal 1
SIGUSR217user-defined signal 2
SIGCLD18 • death of a child
SIGPWR19power-fail restart
SIGWIND20 • window change
SIGURG21 • urgent condition on an I/O channel
SIGIO22 • pollable event occured
SIGSTOP23 † sendable stop signal, not from tty
SIGTSTP24 † stop signal from tty
SIGTTIN25 † process stop by background tty read
SIGTTOU26 † process stop by background tty write
SIGCONT27 • continue a stopped process
SIGXCPU28exceeded CPU time limit
SIGXFSZ29exceeded file size limit
SIGVTALRM30virtual time alarm
SIGPROF31profiling time alarm

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 handler routine to catch signals can be delared as follows:

handler(sig, code, junk, context)
int sig, code, junk
struct sigcontext ∗context;

Here, sig is the signal number. code is a value which further interprets sig; it may be one of the following:

SIGFPE

0: integer overflow
1: floating exception

SIGTRAP

CAUSESINGLE: single step
CAUSEBREAK: breakpoint instruction

The value of junk is the address of the handler routine itself. context is a pointer to the machine state at the time of the exception. It is defined in /usr/include/sys/signal.h.

On floating point exceptions, the FPU is halted. Explicit user action of restarting the FPU will be necessary.

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 fails and no new signal handler is 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).

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