Get State Save/Restore Addresses

Returns the addresses of two procedures used to save and
restore the state of the current task's registers in the
mode which is not currently executing.

Call With:

   AX     = 0305H

Returns:

   Carry flag = clear (this function always succeeds)
   AX     = size of buffer in bytes required to save state
   BX:CX  = real mode address of routine used to
           save/restore state
   SI:(E)DI= protected mode address of routine used to
           save/restore state

Notes:

o  The real mode address returned by this function in BX:CX
   is called only in real mode to save/restore the state of
   the protected mode registers.  The protected mode address
   returned by this function in SI:(E)DI  is called only in
   protected mode to save/restore the state of the real mode
   registers; 16-bit programs should call the address in
   SI:DI, 32-bit programs should call the address in SI:EDI.
   Registers for the current mode can be saved by simply
   pushing them on the stack.
o  Both of the state-save procedures are entered by a FAR
   CALL with the following parameters:

AL = 0 to save state
   = 1 to restore state
ES:(E)DI= (selector or segment):offset of state-save buffer

The state-save buffer must be at least as large as the value returned
   in AX by Int 31H Fn 0305H.  The state save/restore
   procedures do not modify any registers.  For a further
   discussion of use of the state save/restore procedures,
   see page 25.
o  Some DPMI hosts will not require the state to be saved,
   indicating this by returning a buffer size of zero in AX.
   In such cases, the addresses returned by this function
   can still be called, although they will simply return
   without performing any useful function.
o  Clients do not need to call the state save/restore
   procedures before using Int 31H Functions 0300H, 0301H,
   or 0302H.  The state save/restore procedures are provided
   specifically for clients that use the raw mode switch
   services.
o  A client can use the function to save its state in the
   destination mode before switching modes using the raw
   mode switch or issuing real-mode calls from a protected
   mode hardware interrupt handler. Refer to page 24 for the
   detailed information on stacks and mode switching.