Set Descriptor

Copies the contents of an 8-byte buffer into the LDT
descriptor for the specified selector.

Call With:

   AX     = 000CH
   BX     = selector
   ES:(E)DI= selector:offset of 8-byte buffer containing
           descriptor

Returns:

   if function successful
   Carry flag= clear

   if function unsuccessful
   Carry flag= set
   AX     = error code
           8021H   invalid value (access rights/type byte
                   invalid)
           8022H   invalid selector
           8025H   invalid linear address (descriptor
                   references a linear address range outside
                   that allowed for DPMI clients)

Notes:

o  32-bit programs must use ES:EDI to point to the buffer.
   16-bit programs should use ES:DI.
o  The descriptor's access rights/type byte (byte 5) follows
   the same format and restrictions as the access
   rights/type parameter (in CL) for the Set Descriptor
   Access R
ights function (Int 31H Fn 0009H).  On 80386 (or later)
   machines, the descriptor's extended access rights/type
   byte (byte 6) follows the same format and restrictions as
   the extended access rights/type parameter (in CH) for the
   same function, except the low-order 4 bits (marked
   "reserved") are used to set the upper 4 bits of the
   descriptor's limit.
o  If the descriptor's present bit is not set, then the only
   error checking is that the client's CPL must be equal to
   the descriptor's DPL field and the "must be 1" bit in the
   descriptor's byte 5 must be set.
o  A DPMI 1.0 host will reload any segment register which
   contains a selector specified in register BX.  It is
   suggested that DPMI 0.9 hosts also implement this.

o  Refer to the rules for descriptor usage in Appendix D.