how to use 'KBUILD_SRC' in Linux kernel Makefile

[kai yang]

I want to compily the Linux kernel 2.6 kernel in an alternate place
and do not use the Makefile in top directory of kernel. (not different
output directory)
So I want to modify a makefile from Linux kernel 2.6 Makefile, but it
seens not so easy to me, becaust many rules in Makefile(in top level
directory or oher directory like /arch/arm/Makefile) use the PATH only
available in CURRENT DIRECTORY. I want to modify only one Makefile and
don't affect others.

I notice that there is a tag in kernel Makefile: KBUILD_SRC, is that
useful for me? But I didn't get how to use this tag and the Makefile
only says:

    # KBUILD_SRC is set on invocation of make in OBJ directory
    # KBUILD_SRC is not intended to be used by the regular user (for now)

Who can tell me how to use it? Thanks very much!
Did anyone do the same job before? Or is there any other to solve my problem?

Thanks again!!!


--
Best wishes

Everest