Unable to build kernel module with kernel sources from linuxkit/kernel:4.19.76

[etherai]

Expected behavior

Attempting to build kernel module results in a kernel module that cannot be inserted.

# modprobe wireguard
modprobe: can't load module wireguard (extra/wireguard.ko): invalid module format

Issue description here: linuxkit/linuxkit#3402

In the above issue I found https://hub.docker.com/r/docker/for-desktop-kernel/tags?page=1&name=4.19.76

but it is not clear which container has the sources that match the kernel that is shipping with Docker for Windows. I tried a couple and still got the magic version mismatch error on attempting to load the module.

Thanks for the guidance!

Actual behavior

It should be obvious which kernel headers I should be building against.

Information

• Windows Version: Windows 10
• Docker Desktop Version: 2.2.0.4
• Are you running inside a virtualized Windows e.g. on a cloud server or on a mac VM No

[djs55]

Thanks for your report. It's not currently obvious which image corresponds to which version -- I'll have to think about where to put that information.

In kernel 2.2.0.4 the kernel is https://hub.docker.com/layers/docker/for-desktop-kernel/4.19.76-d665d2cbc4fe70f8ab08ba2cd82d052e41d2a704-amd64/images/sha256-c42bff3d5f285dcb1dde0937a8b99e2f51f1f764bd9b847c5d188fd02bb74136?context=explore

To look inside and see the headers + source:

$ docker pull docker/for-desktop-kernel:4.19.76-d665d2cbc4fe70f8ab08ba2cd82d052e41d2a704-amd64
$ docker create --name linux docker/for-desktop-kernel:4.19.76-d665d2cbc4fe70f8ab08ba2cd82d052e41d2a704-amd64 /bin/sh
$ docker cp linux:/ .
$ ls
System.map		intel-ucode-license.txt	kernel-dev.tar		kernel.tar		sys
dev			intel-ucode.cpio	kernel-headers.tar	linux.tar.xz		wireguard.tar.xz
etc			kernel			kernel-source-info	proc

That should be enough to completely recompile the kernel. To make a loadable module I'm not 100% sure as there may be an interaction with the RANDSTRUCT stuff -- let me know how you get on and if there is more info needed.

In future we'd like to use a linuxkit 5.4 kernel directly -- this 4.19 has a couple of backports: mostly FUSE bugfixes plus the virtio-blk DISCARD implementation.

[etherai]

Thank you, @djs55! With that kernel image I was able to successfully build a working kernel module.

[djs55]

@etherai thanks for the confirmation, and sorry for the hassle!

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