copy extended memory.

[Adam Sulmicki]

hello,
    can anyone point me to an documenation on bios's
    interrupt 15, ah=87. It is 'copy extended memory'.

I suspect the implementation I have is  wrong, and
    thus stops me from adding support for legacy
    applications under LinuxBIOS.

Going over phoenix manual and Ralf Browns's
    interrupt list, I know that

CX     = counter
    ES:SI  = pointer to GDT

what is not clear to me is what does determine source and destination
of the copy. Would it just copy between first and second segment
(if so why it is not documented).