# 2.11BSD#431 - /usr/man/cat3/signal.0

    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

    Printed 11/26/99	  May 20, 1986				1

    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

    Printed 11/26/99	  May 20, 1986				2

    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

    Printed 11/26/99	  May 20, 1986				3

    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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