sigstack(2) — DG/UX R4.11MU05



sigstack(2)                    DG/UX R4.11MU05                   sigstack(2)


NAME
       sigstack - set and/or get signal stack context

SYNOPSIS
       #include <signal.h>

       int    sigstack (new_signal_stack, old_signal_stack)
       struct sigstack * new_signal_stack;
       struct sigstack * old_signal_stack;

   where:
       new_signal_stack    NULL or address of new signal stack context
                           specifier

       old_signal_stack    NULL or address of old signal stack context
                           specifier

DESCRIPTION
       Sigstack is used to install a new signal stack context and retrieve
       the previous signal stack context.  A new signal stack context is
       optionally installed using the new_signal_stack parameter.  If
       new_signal_stack is NULL, the signal stack context remains unchanged.
       Otherwise, new_signal_stack is installed.  The previous signal stack
       context may be obtained by the old_signal_stack parameter.  If
       old_signal_stack is NULL, the previous signal stack context is not
       returned.  Otherwise, the previous signal stack context information
       is stored in the location pointed to by old_signal_stack.

       A signal stack is an alternate execution stack on which signals are
       processed.  The signal stack context consists of two components:  the
       address of the base of the signal stack (ss_sp) and an indication as
       to whether the process is currently executing on the signal stack
       (ss_onstack).

       In DG/UX, the user's stack grows from high to low addresses.
       Therefore, the stack pointer, ss_sp, must be the upper bound of the
       memory allocated for the alternate signal stack.  The caller must
       make this adjustment; it will not be made by the system.

       When a signal's action is `catch' and its signal stack choice
       specifies the signal stack, the system checks to see if the process
       is currently executing on the signal 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.

       Signal stacks do not increase automatically, as is done for the
       normal stack.  If the stack overflows unpredictable results may
       occur.

       Sigstack will fail and the signal stack context will be unchanged if
       an error occurs.

ACCESS CONTROL
       None.

RETURN VALUE
       0      Completed successfully.

       -1     An error occurred.  errno is set to indicate the error.

DIAGNOSTICS
       Errno may be set to the following error code:

       EFAULT    Either new_signal_stack or old_signal_stack points to
                 memory which is not a valid part of the process address
                 space.  The validity of the signal stack is not checked.

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


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