sigstack(2)                                           sigstack(2)



     NAME
          sigstack - set or get signal stack context

     SYNOPSIS
          #include <signal.h>

          struct sigstack {
              caddr_t    ss_sp;
              int ss_onstack;
          };

          int sigstack(ss, oss);
          struct sigstack *ss, *oss;

     DESCRIPTION
          sigstack allows users to define an alternate stack on which
          signals are to be processed.  If ss is nonzero, it specifies
          a signal stack on which to deliver signals and tells the
          system if the process is currently executing on that stack.
          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.
          If oss is nonzero, the current signal stack state is re-
          turned.

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

     RETURN VALUE
          Upon successful completion, a value of 0 is returned.  Oth-
          erwise, a value of -1 is returned and errno is set to indi-
          cate the error.

     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.

     SEE ALSO
          sigvec(2), setjmp(3), signal(3).








     April, 1990                                                     1