On Alpha and Integrity server systems, allows a process to change
    the fault characteristic on a page or range of pages.

    Format

      SYS$SETFLT  inadr ,[retadr] ,[acmode] ,fault_flag

    C Prototype

      int sys$setflt  (struct _va_range *inadr, struct _va_range

                      *retadr, unsigned int acmode, unsigned int

                      fault_flag);

1  –  Arguments

 inadr

    OpenVMS usage:address_range
    type:         longword (unsigned)
    access:       read only
    mechanism:    by reference
    Starting and ending virtual addresses of the range of pages whose
    fault characteristic is to be changed. The inadr argument is the
    address of a 2-longword array containing, in order, the starting
    and ending process virtual addresses.

    Addresses are adjusted up or down to fall on CPU-specific page
    boundaries. Only the virtual page number portion of each virtual
    address is used; the low-order byte-within-page bits are ignored.

    If the starting and ending virtual addresses are the same, the
    fault characteristic is changed for a single page.

 retadr

    OpenVMS usage:address_range
    type:         longword (unsigned)
    access:       write only
    mechanism:    by reference-array reference or descriptor
    Starting and ending virtual addresses of the range of pages whose
    fault characteristic was actually changed by $SETFLT. The retadr
    argument is the address of a 2-longword array containing, in
    order, the starting and ending process virtual addresses.

    If an error occurs while the fault characteristic is being
    changed, $SETFLT writes into retadr the range of pages that were
    successfully changed before the error occurred. If no pages were
    affected before the error occurred, $SETFLT writes the value -1
    into each longword of the 2-longword array.

 acmode

    OpenVMS usage:access_mode
    type:         longword (unsigned)
    access:       read only
    mechanism:    by value
    Access mode associated with the call to $SETFLT. The acmode
    argument is a longword containing the access mode. The $PSLDEF
    macro defines symbols for the access modes.

    The $SETFLT service uses whichever of the following two access
    modes is less privileged: (1)  the access mode specified by
    acmode or (2)  the access mode of the caller. To change the fault
    characteristic of any page in the specified range, the resultant
    access mode must be equal to or more privileged than the access
    mode of the owner of that page.

 fault_flag

    OpenVMS usage:mask_longword
    type:         longword (unsigned)
    access:       read only
    mechanism:    by value
    Flag mask specifying the request options. The fault_flag argument
    is a longword bit vector in which each bit corresponds to a flag.
    The $FLTDEF macro and the FLTDEF.H file define a symbolic name
    for each flag.

    The $FLTDEF macro defines the following symbolic names for the
    fault characteristic codes:

    Symbol             Description

    FLT$M_NO_EXECUTE   Fault on execute access attempt
    FLT$M_EXECUTABLE   Allow execute access

    If you specify the fault characteristic as the value 0, the
    characteristic defaults to no execute access.