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#include <signal.h>
int sigvec(sig, vec, ovec) int sig; struct sigvec *vec, *ovec;
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_ONSTACK 0x0001 /* take signal on signal stack */ #define SV_INTERRUPT 0x0002 /* do not restart system on signal return */ #define SV_RESETHAND 0x0004 /* 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>:
SIGHUP(1)hangup SIGINT(2)interrupt SIGQUIT(3)quit SIGILL(4)illegal SIGTRAP(5)trace SIGABRT(6)abort SIGEMT(7)emulator SIGFPE(8)arithmetic SIGKILL(9)kill(cannot SIGBUS(1)*bus SIGSEGV(1)*segmentation SIGSYS(1)*bad SIGPIPE(1)write SIGALRM(1)alarm SIGTERM(1)software SIGURG(1)+urgent SIGSTOP(1)**stop SIGTSTP(1)**stop SIGCONT(1)+continue SIGCHLD(2)+child SIGTTIN(2)**background SIGTTOU(2)**background 23+I/O SIGXCPU(2)cpu getrlimit.2 SIGXFSZ(2)file getrlimit.2 SIGVTALRM(2)virtual getitimer.2 SIGPROF(2)profiling getitimer.2 28+window SIGLOST(2)*resource lockd.8c SIGUSR1(3)user-defined SIGUSR2(3)user-defined
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:
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.
The following defines the codes for signals which produce them. All of these symbols are defined in signal.h:
Condition Signal Code Sun codes: Illegal instruction SIGILL ILL_INSTR_FAULT Integer division by zero SIGFPE FPE_INTDIV_TRAP IEEE floating pt inexact SIGFPE FPE_FLTINEX_TRAP IEEE floating pt division by zero SIGFPE FPE_FLTDIV_TRAP IEEE floating pt underflow SIGFPE FPE_FLTUND_TRAP IEEE floating pt operand error SIGFPE FPE_FLTOPERR_TRAP IEEE floating pt overflow SIGFPE FPE_FLTOVF_FAULT Hardware bus error SIGBUS BUS_HWERR Address alignment error SIGBUS BUS_ALIGN No mapping fault SIGSEGV SEGV_NOMAP Protection fault SIGSEGV SEGV_PROT Object error SIGSEGV SEGV_CODE(code)=SEGV_OBJERR Object error number SIGSEGV SEGV_ERRNO(code) SPARC codes: Privileged instruction violation SIGILL ILL_PRIVINSTR_FAULT Bad stack SIGILL ILL_STACK Trap #n (1 <= n <= 127) SIGILL ILL_TRAP_FAULT(n) Integer overflow SIGFPE FPE_INTOVF_TRAP Tag overflow SIGEMT EMT_TAG MC680X0 codes: Privilege violation SIGILL ILL_PRIVVIO_FAULT Coprocessor protocol error SIGILL ILL_INSTR_FAULT Trap #n (1 <= n <= 14) SIGILL ILL_TRAPn _FAULT A-line op code SIGEMT EMT_EMU1010 F-line op code SIGEMT EMT_EMU1111 CHK or CHK2 instruction SIGFPE FPE_CHKINST_TRAP TRAPV or TRAPcc or cpTRAPcc SIGFPE FPE_TRAPV_TRAP IEEE floating pt compare unordered SIGFPE FPE_FLTBSUN_TRAP IEEE floating pt signaling NaN SIGFPE FPE_FLTNAN_TRAP
The addr signal handler parameter is defined as follows:
Signal Code Addr Sun: SIGILL Any address of faulted instruction SIGEMT Any address of faulted instruction SIGFPE Any address of faulted instruction SIGBUS BUS_HWERR address that caused fault SIGSEGV Any address that caused fault SPARC: SIGBUS BUS_ALIGN address of faulted instruction MC680X0: SIGBUS BUS_ALIGN address 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.
sigvec() returns:
sigvec() will fail and no new signal handler will be installed if one of the following occurs:
An attempt was made to ignore or supply a handler for SIGKILL or SIGSTOP.
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.
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Created by unroff & hp-tools. © somebody (See intro for details). All Rights Reserved. Last modified 11/5/97