how to combine out-of-tree kernel module with EXTERNALSRC kernel source?

Robert P. J. Day

currently have a perfectly functioning zeus-based layer with a
small number of out-of-tree kernel modules which build just fine

$ bitbake kernel-module-fubar

against the stock linux-yocto (5.2) kernel provided by zeus.

was just asked how to build those same out-of-tree modules
against an external kernel identified by (i'm guessing)
EXTERNALSRC. i don't need to build the kernel itself, just
configure it to the point (a la "make modules_prepare") so
that i can build modules against it.

specifying an external source for the kernel seems easy
enough, but i don't see how to then get the modules to
build against that. a quick google showed me:

"Depending on the type of build (eg, 'inherit module' for out
of tree Linux kernel modules) you may or may not need to set

that explanation seems a bit on the vague side ... is there
an explanation of this somewhere? i can't modify recipes, i
need to do this exclusively through local.conf.

thoughts? this seems like a useful enough operation that
surely others have done it before now.


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