SIGNAL(3C)	    UNIX Programmer's Manual	       SIGNAL(3C)


NAME
     signal - simplified software signal facilities

SYNOPSIS
     #include <signal.h>

     (*signal(sig, func))()
     int (*func)();

DESCRIPTION
     Signal is a simplified interface to the more general
     sigvec(2) facility.

     A signal is generated by some abnormal event, initiated by a
     user at a terminal (quit, interrupt, stop), by a program
     error (bus error, etc.), by request of another program
     (kill), or when a process is stopped because it wishes to
     access its control terminal while in the background (see
     tty(4)).  Signals are optionally generated when a process
     resumes after being stopped, when the status of child
     processes changes, or when input is ready at the control
     terminal.	Most signals cause termination of the receiving
     process if no action is taken; some signals instead cause
     the process receiving them to be stopped, or are simply dis-
     carded if the process has not requested otherwise.  Except
     for the SIGKILL and SIGSTOP signals, the signal call allows
     signals either to be ignored or to cause an interrupt to a
     specified location.  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 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 or ignored)
     SIGTSTP   18'|+'stop signal generated from keyboard
     SIGCONT   19@  continue after stop
     SIGCHLD   20@  child status has changed
     SIGTTIN   21'|+'background read attempted from control terminal
     SIGTTOU   22'|+'background write attempted to control terminal


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SIGNAL(3C)	    UNIX Programmer's Manual	       SIGNAL(3C)


     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.

     If func is SIG_DFL, the default action for signal sig is
     reinstated; 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 func is SIG_IGN the signal is subsequently ignored and
     pending instances of the signal are discarded.  Otherwise,
     when the signal occurs further occurrences of the signal are
     automatically blocked and func is called.

     A return from the function unblocks the handled signal and
     continues the process at the point it was interrupted.
     Unlike previous signal facilities, the handler func remains
     installed after a signal has been delivered.

     If a caught signal occurs during certain system calls, caus-
     ing the call to terminate prematurely, the call is automati-
     cally 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).

     The value of signal is the previous (or initial) value of
     func for the particular signal.

     After a fork(2) or vfork(2) the child inherits all signals.
     Execve(2) resets all caught signals to the default action;
     ignored signals remain ignored.

RETURN VALUE
     The previous action is returned on a successful call.  Oth-
     erwise, -1 is returned and errno is set to indicate the
     error.

ERRORS
     Signal will fail and no action will take place if one of the
     following occur:

     [EINVAL]	    Sig is not a valid signal number.

     [EINVAL]	    An attempt is made to ignore or supply a


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SIGNAL(3C)	    UNIX Programmer's Manual	       SIGNAL(3C)


		    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), sigvec(2), sigblock(2), sigset-
     mask(2), sigpause(2), sigstack(2), setjmp(3), tty(4)

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

	 handler(sig, code, scp)

     Here sig is the signal number, into which the hardware
     faults and traps are mapped as defined below.  Code is a
     parameter which is either a constant as given below or, for
     compatibility mode faults, the code provided by the
     hardware. Scp is a pointer to the struct sigcontext used by
     the system to restore the process context from before the
     signal.  Compatibility mode faults are distinguished from
     the other SIGILL traps by having PSL_CM set in the psl.

     The following defines the mapping of hardware traps to sig-
     nals 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


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SIGNAL(3C)	    UNIX Programmer's Manual	       SIGNAL(3C)


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 constant 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 sig-
     nals 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 compiler for handler
     routines written in C automatically saves the remaining gen-
     eral 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.


Printed 11/26/99	  May 20, 1986				4


 
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