sigstack(3)             (BSD Compatibility Package)             sigstack(3)


   NAME
         sigstack - set and/or get signal stack context

   SYNOPSIS
         cc [ flag... ] file ... -lucb

         #include <signal.h>

         int sigstack (ss, oss)
         struct sigstack *ss, *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(2) 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.

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




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   sigstack(3)             (BSD Compatibility Package)             sigstack(3)


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

   SEE ALSO
         sigvec(3), signal(3)

         sigaltstack(2), in the Programmer's Reference Manual.

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









































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