INT 2C P - RM386 v6.00 - CLOAKING - SET PASSALONG ADDRESS
        AX = 0009h
        DX:EBX = new value for passalong address
Return: CF clear
Note:   when an INT 2C instruction is executed in V86 mode, RM386 calls the
          passalong address.  The handler should check whether the upcall
          is of interest to it, and if not it should jump to the old passalong
          address (retrieved with AX=0008h before the handler was installed)
SeeAlso: AX=0008h,AX=002Dh,INT 2C"CLOAKING"

Passalong address called with:
        EAX = CS:IP of byte following INT 2C instruction invoking passalong
        SS:EBX -> caller registers (see below)
        CF clear
        others undefined
Return: CF clear: pass along to V86-mode INT 2C handler
        CF set: return immediately to V86 mode

Format of caller registers:
Offset  Size    Description
 00h    DWORD   EDI
 04h    DWORD   ESI
 08h    DWORD   EBP
 0Ch    DWORD   reserved (ESP from PUSHAD instruction)
 10h    DWORD   EBX
 14h    DWORD   EDX
 18h    DWORD   ECX
 1Ch    DWORD   EAX
 20h    DWORD   error code
 24h    DWORD   EIP
 28h    WORD    CS
 2Ah    WORD    padding
 2Ch    DWORD   EFLAGS
 30h    DWORD   ESP
 34h    WORD    SS
 36h    WORD    padding
--remainder not available if protected-mode ring3 trap---
 38h    WORD    ES
 3Ah    WORD    padding
 3Ch    WORD    DS
 3Eh    WORD    padding
 40h    WORD    FS
 42h    WORD    padding
 44h    WORD    GS
 46h    WORD    padding

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