sigstack(2)                                                     sigstack(2)
                               TO BE OBSOLETED



 NAME    [Toc]    [Back]
      sigstack - set and/or get alternate signal stack context

 SYNOPSIS    [Toc]    [Back]
      #include <signal.h>

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

 DESCRIPTION    [Toc]    [Back]
      The sigstack() function allows the calling process to indicate to the
      system an area of its address space to be used for processing signals
      received by the process.

      The sigstack() function requires the application to have knowledge of
      the underlying system's stack architecture.  To ensure portability,
      use sigaltstack() instead of sigstack() when writing or rewriting
      applications.

      If the ss argument is not a null pointer, it  must point to a sigstack
      structure.  The length of the application-supplied stack must be at
      least SIGSTKSZ bytes.  If the alternate signal stack overflows, the
      resulting behavior is undefined.  (See APPLICATION USAGE below.)

           +  The value of the ss_onstack member indicates whether the
              process wants the system to use an alternate signal stack when
              delivering signals.

           +  The value of the ss_sp member indicates the desired location
              of the alternate signal stack area in the process' address
              space.

           +  If the ss argument is a null pointer, the current alternate
              signal stack context is not changed.

      If the oss argument is not a null pointer, it points to a sigstack
      structure in which the current alternate signal stack context is
      placed.  The value stored in the ss_onstack member of oss will be nonzero
 if the process is currently executing on the alternate signal
      stack.  If the oss argument is a null pointer, the current alternate
      signal stack context is not returned.

      When a signal's action indicates its handler should execute on the
      alternate signal stack (specified by calling sigaction()), the
      implementation checks to see if the process is currently executing on
      that stack.  If the process is not currently executing on the
      alternate signal stack, the system arranges a switch to the alternate
      signal stack for the duration of the signal handler's execution.




 Hewlett-Packard Company            - 1 -   HP-UX 11i Version 2: August 2003






 sigstack(2)                                                     sigstack(2)
                               TO BE OBSOLETED



      After a successful call to one of the exec() functions, there are no
      alternate signal stacks in the new process image.

      The correct use of sigstack() is hardware dependent, and therefore is
      not portable between different HP-UX implementations.  sigspace() is
      portable between different HP-UX implementations and should be used
      when the application does not need to know where the signal stack is
      located (see sigspace(2)).  sigstack() is provided for compatibility
      with other systems that provide this functionality.  Users should note
      that there is no guarantee that functionality similar to this is even
      possible on some architectures.

      The sigstack() function is scheduled to be withdrawn from a future
      version of the Single UNIX Specification.  The sigaltstack() function
      is the recommended replacement.  Refer to the sigaltstack(2) reference
      page.

 RETURN VALUE    [Toc]    [Back]
      The sigstack() function returns the following:

           0              Success.

           -1             Failure: errno is set to indicate the error.

 ERRORS    [Toc]    [Back]
      The sigstack() function will fail if:

           [EPERM]        An attempt was made to modify an active stack or
                          an active alternate stack.

           [EFAULT]       Either of ss or oss is not a null pointer and
                          points outside the allocated address space of the
                          process.  This error is not reliably detected.

 WARNINGS    [Toc]    [Back]
      Do not use sigstack() in conjunction with sigspace().

      The direction of stack growth is not indicated in the historical
      definition of struct sigstack.  The only way to portably establish a
      stack pointer is for the application to determine stack growth
      direction, or to allocate a block of storage and set the stack pointer
      to the middle.  An application can assume that the size of the signal
      stack is SIGSTKSZ.  To specify a signal stack size other than
      SIGSTKSZ, use the sigaltstack() function.

      Leaving the context of a service routine abnormally, such as by
      longjmp() (see setjmp(3C)), might remove the guarantee that the
      ordinary execution of the program does not extend into the guaranteed
      space.  It might also cause the program to lose forever its ability to
      automatically increase the stack size, causing the program to be
      limited to the guaranteed space.



 Hewlett-Packard Company            - 2 -   HP-UX 11i Version 2: August 2003






 sigstack(2)                                                     sigstack(2)
                               TO BE OBSOLETED



      In HP-UX release 11.i, use of sigstack() in threads created with
      process contention scope could result in undefined behavior.  This
      function will continue to be reliable in threads created with system
      contention scope.

    Obsolescent Interfaces    [Toc]    [Back]
      sigstack() is to be obsoleted at a future date.

 APPLICATION USAGE    [Toc]    [Back]
      A portable application, when being written or rewritten, should use
      sigaltstack() instead of sigstack().

      On some implementations, stack space is automatically extended as
      needed.  On those implementations, automatic extension is typically
      not available for an alternate stack.  If a signal stack overflows,
      the resulting behavior of the process is undefined.

      The direction of stack growth is not indicated in the historical
      definition of struct sigstack.  The only way to portably establish a
      stack pointer is for the application to determine stack growth
      direction, or to allocate a block of storage and set the stack pointer
      to the middle.  The implementation may assume that the size of the
      signal stack is SIGSTKSZ as found in <signal.h>.  An implementation
      that would like to specify a signal stack size other than SIGSTKSZ
      should use sigaltstack().

      Programs should not use longjmp() to leave a signal handler that is
      running on a stack established with sigstack().  Doing so may disable
      future use of the signal stack.  For abnormal exit from a signal
      handler, siglongjmp(), setcontext(), or swapcontext() may be used.
      These functions fully support switching from one stack to another.

    Threads Considerations    [Toc]    [Back]
      Each thread (with system contention scope) may define an alternate
      signal handling stack.

 AUTHOR    [Toc]    [Back]
      sigstack() was developed by HP and the University of California,
      Berkeley.

 SEE ALSO    [Toc]    [Back]
      exec(2), fork(2), setjmp(3C), sigaltstack(2), sigspace(2), signal(5),
      sigaction(2).

 CHANGE HISTORY    [Toc]    [Back]
      First released in Issue 4, Version 2.


 Hewlett-Packard Company            - 3 -   HP-UX 11i Version 2: August 2003