SIGVEC(2) — SYSTEM CALLS

NAME

sigvec − software signal facilities

SYNOPSIS

#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 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 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 mask specified in vec is not allowed to block SIGKILL, SIGSTOP, or SIGCONT. The system enforces this restriction silently.

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

SIGHUP1hangup
SIGINT2interrupt
SIGQUIT3∗quit
SIGILL4∗illegal instruction (other than A-line or F-line op code)
SIGTRAP5∗trace trap
SIGIOT6∗IOT instruction (not generated on Suns)
SIGEMT7∗EMT instruction (A-line or F-line op code)
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
SIGURG16urgent condition present on socket
SIGSTOP17†stop (cannot be caught, blocked, or ignored)
SIGTSTP18†stop signal generated from keyboard
SIGCONT19•continue after stop (cannot be blocked)
SIGCHLD20•child status has changed
SIGTTIN21†background read attempted from control terminal
SIGTTOU22†background write attempted to control terminal
SIGIO23i/o is possible on a descriptor (see
fcntl(2))
SIGXCPU24cpu time limit exceeded (see
setrlimit(2))
SIGXFSZ25file size limit exceeded (see
setrlimit(2))
SIGVTALRM26virtual time alarm (see
setitimer(2))
SIGPROF27profiling timer alarm (see
setitimer(2))
SIGWINCH28•window changed (see
win(4S))

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, causing the call to terminate prematurely, the call is automatically restarted. In particular this can 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.

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

NOTES

The handler routine can be declared:

    handler(sig, code, scp)
    int sig, code;
    struct sigcontext ∗scp;

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.

Programs that must be portable to UNIX systems other than 4.2 BSD should use the signal(3) interface instead.

CODES

The following defines the codes for signals which produce them. All of these symbols are defined in <signal.h>:

Hardware conditionSignalCode
Illegal instructionSIGILLILL_INSTR_FAULT
Privilege violationSIGILLILL_PRIVVIO_FAULT
Coprocessor protocol errorSIGILLILL_INSTR_FAULT
Trap #n (1 <= n <= 14)SIGILLILL_TRAPn_FAULT
^ ^ n’s above should be italicized ^
A-line op codeSIGEMTEMT_EMU1010
F-line op codeSIGEMTEMT_EMU1111
Integer division by zeroSIGFPEFPE_INTDIV_TRAP
CHK or CHK2 instructionSIGFPEFPE_CHKINST_TRAP
TRAPV or TRAPcc or cpTRAPccSIGFPEFPE_TRAPV_TRAP
IEEE floating point compare unorderedSIGFPEFPE_FLTBSUN_TRAP
IEEE floating point inexactSIGFPEFPE_FLTINEX_TRAP
IEEE floating point division by zeroSIGFPEFPE_FLTDIV_TRAP
IEEE floating point underflowSIGFPEFPE_FLTUND_TRAP
IEEE floating point operand errorSIGFPEFPE_FLTOPERR_TRAP
IEEE floating point overflowSIGFPEFPE_FLTOVF_FAULT
IEEE floating point signaling NaNSIGFPEFPE_FLTNAN_TRAP

RETURN VALUE

A 0 value indicated that the call succeeded. A −1 return value indicates 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 points to memory which 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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