sigstack(3BSD)       (BSD System Compatibility)       sigstack(3BSD)


       NAME
             sigstack - (BSD) set and/or get signal stack context

       SYNOPSIS
             /usr/ucb/cc [flag . . . ] file . . .
             #include <signal.h>
             int sigstack (struct sigstack *ss, struct sigstack *oss);

       DESCRIPTION
             sigstack allows users to define an alternate stack, called the
             ``signal stack,'' on which signals are to be processed.  When
             a signal's action indicates its handler should execute on the
             signal stack (specified with a sigvec(3BSD) call), the system
             checks to see if the process is currently executing on that
             stack.  If the process is not currently executing on the
             signal stack, the system arranges a switch to the signal stack
             for the duration of the signal handler's execution.

             A signal stack is specified by a sigstack structure, which
             includes the following members:

                   char      *ss_sp;        /* signal stack pointer */
                   int       ss_onstack;    /* current status */

             ss_sp is the initial value to be assigned to the stack pointer
             when the system switches the process to the signal stack.
             Note that, on machines where the stack grows downwards in
             memory, this is not the address of the beginning of the signal
             stack area.  ss_onstack field is zero or non-zero depending on
             whether the process is currently executing on the signal stack
             or not.

             If ss is not a NULL pointer, sigstack sets the signal stack
             state to the value in the sigstack structure pointed to by ss.
             Note: if ss_onstack is non-zero, the system will think that
             the process is executing on the signal stack.  If ss is a NULL
             pointer, the signal stack state will be unchanged.  If oss is
             not a NULL pointer, the current signal stack state is stored
             in the sigstack structure pointed to by oss.

       RETURN VALUE
             Upon successful completion, a value of 0 is returned.
             Otherwise, a value of -1 is returned and errno is set to
             indicate the error.




                           Copyright 1994 Novell, Inc.               Page 1

      sigstack(3BSD)       (BSD System Compatibility)       sigstack(3BSD)


      ERRORS
            sigstack will fail and the signal stack context will remain
            unchanged if one of the following occurs.

            EFAULT         Either ss or oss points to memory that is not a
                           valid part of the process address space.

      REFERENCES
            sigaltstack(2), signal(3BSD), sigvec(3BSD)

      NOTICES
            Signal stacks are not ``grown'' automatically, as is done for
            the normal stack.  If the stack overflows unpredictable
            results may occur.


































                          Copyright 1994 Novell, Inc.               Page 2