Compile external module against linux source and use functionality in linux source

[Valdis.Kletnieks at vt.edu]

On Thu, 25 Sep 2014 10:49:33 +0530, Arjun Pandey said:

> Step 1 goes through fine. The module gets compiled fine.
> However now when i try to compile the kernel i get linker error of
> undefined reference to the function exported from the kernel module.
>
> I can't find any documentation on this usecase.

In general, things that are built-into the kernel with CONFIG_FOO=y
are *not* allowed or able to reference symbols that are in a module.

This is because a module can potentially not be loaded (consider system
boot before you're up far enough to do a modprobe, as an important
special case), at which point trying to call the non-existent module
gets you an oops or panic.

So you can't find any doc on it because it's not supported.
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