If you will have time for newbie, to explain in a few words, what is it need
for (whole idea, or key detail), and, maybe, why it is generated so ... interestingly:

            asm-offsets.c -> *.s -> *.h
 (but this looks like interconnecting C and assembler, obviously)

Correct - asm-offsets is used to transfer constants for .c to assembler,
which us especially convinient for constant that differ when a stuct
is changed.

I will glad to help providing solution maybe somewhat earlier (well, i'm
trying to understand whole building process, if that matters).

Basically what is requested is to move the generic parts of asm-offsets
generation from top-level Kbuild file to a generic file somewhere.

Since this is not generic Kbuild functionality but more specific to the
kernel it should not be part of Kbuild generic files.
include/asm-generic/asm-offsets seems to be a fair place for it.

It would contain the sed-y parts as well as cmd_offsets definition.

I would be glad if you could give that a spin.

	Sam