NAME

sigvec − software signal facilities

SYNOPSIS

#include <signal.h>

int 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. 

A process may also specify a set of flags for a signal that affect the delivery of that signal. 

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 ORing in the signal mask associated with the handler to be invoked. 

The action to be taken when the signal is delivered is specified by a sigvec structure, defined in <signal.h> as:

struct sigvec {

void (∗sv_handler)();/∗ signal handler ∗/
int sv_mask;/∗ signal mask to apply ∗/
int sv_flags;/∗ see signal options ∗/

}

The following bits may be set in sv_flags:

#define SV_ONSTACK0x0001/∗ take signal on signal stack ∗/
#define SV_INTERRUPT0x0002/∗ do not restart system on signal return ∗/
#define SV_RESETHAND0x0004/∗ reset signal handler to SIG_DFL on signal ∗/

If the SV_ONSTACK bit is set in the flags for that signal, the system will deliver the signal to the process on the signal stack specified with sigstack(2), rather than delivering the signal on the current stack. 

If vec is not a NULL pointer, sigvec() assigns the handler specified by sv_handler, the mask specified by sv_mask, and the flags specified by sv_flags to the specified signal.  If vec is a NULL pointer, sigvec() does not change the handler, mask, or flags for the specified signal. 

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

If ovec is not a NULL pointer, the handler, mask, and flags in effect for the signal before the call to sigvec() are returned to the user.  A call to sigvec() with vec a NULL pointer and ovec not a NULL pointer can be used to determine the handling information currently in effect for a signal without changing that information. 

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

SIGHUP1hangup
SIGINT2interrupt
SIGQUIT3∗quit
SIGILL4∗illegal instruction
SIGTRAP5∗trace trap
SIGABRT6∗abort (generated by abort(3) routine)
SIGEMT7∗emulator trap
SIGFPE8∗arithmetic exception
SIGKILL9kill (cannot be caught, blocked, or ignored)
SIGBUS10∗bus error
SIGSEGV11∗segmentation violation
SIGSYS12∗bad argument to system call
SIGPIPE13write on a pipe or other socket with no one to read it
SIGALRM14alarm clock
SIGTERM15software termination signal
SIGURG16•urgent condition present on socket
SIGSTOP17†stop (cannot be caught, blocked, or ignored)
SIGTSTP18†stop signal generated from keyboard
SIGCONT19•continue after stop
SIGCHLD20•child status has changed
SIGTTIN21†background read attempted from control terminal
SIGTTOU22†background write attempted to control terminal
SIGIO23•I/O is possible on a descriptor (see fcntl(2V))
SIGXCPU24cpu time limit exceeded (see
getrlimit(2))
SIGXFSZ25file size limit exceeded (see
getrlimit(2))
SIGVTALRM26 virtual time alarm (see
getitimer(2))
SIGPROF27profiling timer alarm (see
getitimer(2))
SIGWINCH28•window changed (see termio(4) and win(4S))
SIGLOST29∗resource lost (see
lockd(8C))
SIGUSR130user-defined signal 1
SIGUSR231user-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(2V) is performed, unless the SV_RESETHAND bit is set in the flags for that signal.  In that case, the value of the handler for the caught signal is set to SIG_DFL before entering the signal-catching function, unless the signal is SIGILL or SIGTRAP.  Also, if this bit is set, the bit for that signal in the signal mask will not be set; unless the signal mask associated with that signal blocks that signal, further occurrences of that signal will not be blocked.  The SV_RESETHAND flag is not available in 4.2BSD, hence it should not be used if backward compatibility is needed. 

The default action for a signal may be reinstated by setting the signal’s handler to SIG_DFL; this default is termination 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 the process is terminated, a “core image” will be made in the current working directory of the receiving process if the signal is one for which an asterisk appears in the above list and the following conditions are met:

• The effective user ID (EUID) and the real user ID (UID) of the receiving process are equal. 

• The effective group ID (EGID) and the real group ID (GID) of the receiving process are equal. 

• An ordinary file named core exists and is writable or can be created.  If the file must be created, it will have the following properties:

• a mode of 0666 modified by the file creation mask (see umask(2V))

• a file owner ID that is the same as the effective user ID of the receiving process. 

• a file group ID that is the same as the file group ID of the current directory

If the handler for that signal is SIG_IGN, the signal is subsequently ignored, and pending instances of the signal are discarded. 

Note: the signals SIGKILL and SIGSTOP cannot be ignored. 

If a caught signal occurs during certain system calls, the call is restarted by default.  The call can be forced to terminate prematurely with an EINTR error return by setting the SV_INTERRUPT bit in the flags for that signal.  SV_INTERRUPT is not available in 4.2BSD, hence it should not be used if backward compatibility is needed.  The affected system calls are read(2V) or write(2V) on a slow device (such as a terminal or pipe or other socket, but not a file) and during a wait(2V). 

After a fork(2V), or vfork(2) the child inherits all signals, the signal mask, the signal stack, and the restart/interrupt and reset-signal-handler flags. 

The execve(2V), call 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. 

CODES

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

ConditionSignalCode
Sun codes:
Illegal instructionSIGILLILL_INSTR_FAULT
Integer division by zeroSIGFPEFPE_INTDIV_TRAP
IEEE floating pt inexactSIGFPEFPE_FLTINEX_TRAP
IEEE floating pt division by zeroSIGFPEFPE_FLTDIV_TRAP
IEEE floating pt underflowSIGFPEFPE_FLTUND_TRAP
IEEE floating pt operand errorSIGFPEFPE_FLTOPERR_TRAP
IEEE floating pt overflowSIGFPEFPE_FLTOVF_FAULT
Hardware bus errorSIGBUSBUS_HWERR
Address alignment errorSIGBUSBUS_ALIGN
No mapping faultSIGSEGVSEGV_NOMAP
Protection faultSIGSEGVSEGV_PROT
Object errorSIGSEGVSEGV_CODE(code)=SEGV_OBJERR
Object error numberSIGSEGVSEGV_ERRNO(code)
SPARC codes:
Privileged instruction violationSIGILLILL_PRIVINSTR_FAULT
Bad stackSIGILLILL_STACK
Trap #n (1 <= n <= 127)SIGILLILL_TRAP_FAULT(n)
Integer overflowSIGFPEFPE_INTOVF_TRAP
Tag overflowSIGEMTEMT_TAG
MC680X0 codes:
Privilege violationSIGILLILL_PRIVVIO_FAULT
Coprocessor protocol errorSIGILLILL_INSTR_FAULT
Trap #n (1 <= n <= 14)SIGILLILL_TRAPn _FAULT
A-line op codeSIGEMTEMT_EMU1010
F-line op codeSIGEMTEMT_EMU1111
CHK or CHK2 instructionSIGFPEFPE_CHKINST_TRAP
TRAPV or TRAPcc or cpTRAPccSIGFPEFPE_TRAPV_TRAP
IEEE floating pt compare unorderedSIGFPEFPE_FLTBSUN_TRAP
IEEE floating pt signaling NaNSIGFPEFPE_FLTNAN_TRAP

ADDR

The addr signal handler parameter is defined as follows:

SignalCodeAddr
Sun:
SIGILLAnyaddress of faulted instruction
SIGEMTAnyaddress of faulted instruction
SIGFPEAnyaddress of faulted instruction
SIGBUSBUS_HWERRaddress that caused fault
SIGSEGVAnyaddress that caused fault
SPARC:
SIGBUSBUS_ALIGNaddress of faulted instruction
MC680X0:
SIGBUSBUS_ALIGNaddress that caused fault

The accuracy of addr is machine dependent.  For example, certain machines may supply an address that is on the same page as the address that caused the fault.  If an appropriate addr cannot be computed it will be set to SIG_NOADDR. 

RETURN VALUES

sigvec() returns:

0 on success. 

−1 on failure and sets errno to indicate the error. 

ERRORS

sigvec() will fail and no new signal handler will be installed if one of the following occurs:

EFAULT Either vec or ovec is not a NULL pointer and points to memory that is not a valid part of the process address space. 

EINVAL Sig is not a valid signal number. 

An attempt was made to ignore or supply a handler for SIGKILL or SIGSTOP. 

SEE ALSO

execve(2V), fcntl(2V), fork(2V), getitimer(2), getrlimit(2), ioctl(2), kill(2V), ptrace(2), read(2V), sigblock(2), sigpause(2V), sigsetmask(2), sigstack(2), umask(2V), vfork(2), wait(2V), write(2V), setjmp(3V), signal(3V), streamio(4), termio(4), win(4S), lockd(8C)

NOTES

SIGPOLL is a synonym for SIGIO.  A SIGIO will be issued when a file descriptor corresponding to a STREAMS (see intro(2)) file has a "selectable" event pending.  Unless that descriptor has been put into asynchronous mode (see fcntl (2V), a process must specifically request that this signal be sent using the I_SETSIG ioctl(2) call (see streamio(4)).  Otherwise, the process will never receive SIGPOLL. 

The handler routine can be declared:

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

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; and addr is additional address information. 

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

Sun Release 4.1  —  Last change: 21 January 1990