However I forgot to copy init script. It is still present in kernel image that I have. How to extract it? Please note that initrd is not a separate file but is in the kernel image.
After unpacking by:
(binoffset.c is in sources of Linux).
Gives the listing of archive. Just after the entry for /init in
Is the contents of script.
It is not perfect solution but at least it seems to work. Please answer if you know 'correct' way (for binaries) easy (not writing long program) - I'm not marking it as solution.