SIGVEC(2)							System Calls Manual							 SIGVEC(2)

NAME

       sigvec - software signal facilities

SYNOPSIS

       #include <signal.h>

       struct sigvec {
       int  (*sv_handler)();
       long sv_mask;
       int  sv_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  han-
       dler  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 deliv-
       ered 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  cur-
       rently  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 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 instruction
       SIGTRAP	 5*   trace trap
       SIGIOT	 6*   IOT instruction
       SIGEMT	 7*   EMT instruction
       SIGFPE	 8*   floating point exception
       SIGKILL	 9    kill (cannot be caught, blocked, or ignored)
       SIGBUS	 10*  bus error
       SIGSEGV	 11*  segmentation violation
       SIGSYS	 12*  bad argument to system call
       SIGPIPE	 13   write on a pipe with no one to read it
       SIGALRM	 14   alarm clock
       SIGTERM	 15   software termination signal
       SIGURG	 16@  urgent condition present on socket
       SIGSTOP	 17|+'stop (cannot be caught, blocked, or ignored)
       SIGTSTP	 18|+'stop signal generated from keyboard
       SIGCONT	 19@  continue after stop (cannot be blocked)
       SIGCHLD	 20@  child status has changed
       SIGTTIN	 21|+'background read attempted from control terminal
       SIGTTOU	 22|+'background write attempted to control terminal
       SIGIO	 23@  i/o is possible on a descriptor (see fcntl(2))
       SIGXCPU	 24   cpu time limit exceeded (see setrlimit(2))
       SIGXFSZ	 25   file size limit exceeded (see setrlimit(2))
       SIGVTALRM 26   virtual time alarm (see setitimer(2))
       SIGPROF	 27   profiling timer alarm (see setitimer(2))
       SIGWINCH  28@  window size change
       SIGUSR1	 30   user defined signal 1
       SIGUSR2	 31   user 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(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 SV_INTERRUPT flag is not available in 4.2BSD, hence it should not be used if backward compatibility is needed.

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 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).

SEE ALSO

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

NOTES  (VAX-11)
       The handler routine can be declared:

	   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 parameter that is either  a
       constant  as  given below or, for compatibility mode faults, the code provided by the hardware (Compatibility mode faults are distinguished
       from the other SIGILL traps by having PSL_CM set in the psl).  Scp is a pointer to the sigcontext structure (defined in	<signal.h>),  used
       to restore the context from before the signal.

       The following defines the mapping of hardware traps to signals and codes.  All of these symbols are defined in <signal.h>:

	  Hardware condition		      Signal	   Code

       Arithmetic traps:
	  Integer overflow		      SIGFPE	   FPE_INTOVF_TRAP
	  Integer division by zero	      SIGFPE	   FPE_INTDIV_TRAP
	  Floating overflow trap	      SIGFPE	   FPE_FLTOVF_TRAP
	  Floating/decimal division by zero   SIGFPE	   FPE_FLTDIV_TRAP
	  Floating underflow trap	      SIGFPE	   FPE_FLTUND_TRAP
	  Decimal overflow trap 	      SIGFPE	   FPE_DECOVF_TRAP
	  Subscript-range		      SIGFPE	   FPE_SUBRNG_TRAP
	  Floating overflow fault	      SIGFPE	   FPE_FLTOVF_FAULT
	  Floating divide by zero fault       SIGFPE	   FPE_FLTDIV_FAULT
	  Floating underflow fault	      SIGFPE	   FPE_FLTUND_FAULT
       Length access control		      SIGSEGV
       Protection violation		      SIGBUS
       Reserved instruction		      SIGILL	   ILL_RESAD_FAULT
       Customer-reserved instr. 	      SIGEMT
       Reserved operand 		      SIGILL	   ILL_PRIVIN_FAULT
       Reserved addressing		      SIGILL	   ILL_RESOP_FAULT
       Trace pending			      SIGTRAP
       Bpt instruction			      SIGTRAP
       Compatibility-mode		      SIGILL	   hardware supplied code
       Chme				      SIGSEGV
       Chms				      SIGSEGV
       Chmu				      SIGSEGV

NOTES  (PDP-11)
       The handler routine can be declared:

	   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 parameter that is a con-
       stant as given below.  Scp is a pointer to the sigcontext structure (defined in <signal.h>), used to restore the context  from  before  the
       signal.

       The following defines the mapping of hardware traps to signals and codes.  All of these symbols are defined in <signal.h>:

	  Hardware condition		      Signal	   Code

       Arithmetic traps:
	  Floating overflow trap	      SIGFPE	   FPE_FLTOVF_TRAP
	  Floating/decimal division by zero   SIGFPE	   FPE_FLTDIV_TRAP
	  Floating underflow trap	      SIGFPE	   FPE_FLTUND_TRAP
	  Decimal overflow trap 	      SIGFPE	   FPE_DECOVF_TRAP
	  Illegal return code		      SIGFPE	   FPE_CRAZY
	  Bad op code			      SIGFPE	   FPE_OPCODE_TRAP
	  Bad operand			      SIGFPE	   FPE_OPERAND_TRAP
	  Maintenance trap		      SIGFPE	   FPE_MAINT_TRAP
       Length access control		      SIGSEGV
       Protection violation (odd address)     SIGBUS
       Reserved instruction		      SIGILL	   ILL_RESAD_FAULT
       Customer-reserved instr. 	      SIGEMT
       Trace pending			      SIGTRAP
       Bpt instruction			      SIGTRAP

       The  handler  routine  must save any registers it uses and restore them before returning.  On the PDP-11, the kernel saves r0 and r1 before
       calling the handler routine, but expect the handler to save any other registers it uses.  The standard entry code generated by the  C  com-
       piler  for  handler  routines written in C automatically saves the remaining general registers, but floating point registers are not saved.
       As a result there is currently no [standard] method for a handler routine written in C to perform floating point operations without blowing
       the interrupted program out of the water.

BUGS

       This manual page is still confusing.

4th Berkeley Distribution					  January 8, 1986							 SIGVEC(2)