Installing Debian kernel headers package does not install all kernel headers

Question

I am currently running the most recent update of Debian bookworm (which I think is built on Linux 6.1.0.32-amd64 or Linux-6.1.129-1, that's what uname -r returns). I have been trying to install a set of modules (linux-gpib to be specific). The INSTALL files for this driver say installing the Debian kernel headers (using sudo apt-get install linux-headers-$(uname -r)) should be sufficient. But when running the Makefile for the kernel part of these modules I saw issues where BTF generation was skipped due to unavailability of vmlinux, and later when I copied vmlinux to the kernel headers directory, another error relating to files relating to a missing directory tools/bpf it was expecting to find in my /lib/modules/$(uname -r) directory.

Looking at the headers I have in usr/src/linux-headers-$(uname -r) and comparing to what I get when I run apt-get source linux-headers-$(uname -r) I see a lot of missing directories. The tools directory in what I have installed is nearly empty (only containing objtool) and has nothing else, while the directory I sourced has a large suite of tools. I have used Ubuntu before and never had this issue with that operating system.

Does Debian by default install a very sparse set of modules and expect you to build the kernel source tree from scratch? And is there a historical reason why vmlinux might have been expected to be in the modules for my current build when it is not there by default? I'm somewhat new to Linux so if anything I've typed seems wrong, please correct me. Thank you so much!

Answer 1

Unless you specifically need BTF information for the modules you’re building (which is unlikely if you’re new to Linux), you can ignore the warnings.

The BPF tools were recently added to the Linux kernel packages for Debian 13 (in 6.12.16-1); I imagine this change will eventually be available in the backported kernel, but not necessarily in the main Debian 12 kernel. The fixed kernel header packages also include vmlinux and depend on additional tools needed for BTF generation (pahole).