Install kernel-headers on target - flexbuild Linux Debian 6.12.49

[sombreminjaben]

Hi,

I am developing a custom out-of-tree Linux module for my IMX8MP-EVK board running Debian Linux (built using the latest version of flexbuild). Currently, to build my module, I added it to the Linux sources, modifying the corresponding Kconfig and Makefile. However, I would like to be able to build my module on-target to make the process faster but there are no kernel-headers installed and I can't seem to find how to get them on target. 

Could anyone guide me on how to build my Debian Linux with kernel-headers installed ?

Thanks.

Benjamin.

[sombreminjaben]

Hi,

Yes I quickly figured that trying apt install linux-headers-$(uname -r) would not give me the right headers.

Thank you for your quick response, I should be able to adopt a workflow that works for me.

[yipingwang · Accepted solution]

For the i.MX8MP-EVK Debian image built with Flexbuild, the practical answer is: do not rely on apt install linux-headers-$(uname -r) on the target . The retrieved NXP material shows Flexbuild builds the kernel, DTBs, modules, boot image, and rootfs, but I did not find an i.MX8MP-specific Flexbuild option that generates and preinstalls a matching linux-headers-* package into the Debian rootfs. The supported/clean workflow is to build your out-of-tree module against the same compiled kernel tree used by Flexbuild, then copy the .ko to the board.

Recommended workflow:

cd flexbuild

. setup.env

bld docker

. setup.env

bld host-dep

# Full image, or at least the kernel

LOG_LEVEL=0 bld -m imx8mpevk

# or:

LOG_LEVEL=0 bld linux -m imx8mpevk

The Debian SDK guide lists bld -m imx8mpevk as the full build command and bld linux -m imx8mpevk as the separate kernel build command; it also says the kernel-related source is under components_lsdk2512/linux/ , and the compiled output is under build_lsdk2512/linux/linux/arm64/IMX for the i.MX platform example.

Then build your external module on the host against that compiled/prepared kernel tree, for example:

obj-m += my_driver.o

KERNEL_SRC ?= /path/to/flexbuild/components_lsdk2512/linux

all:

              $(MAKE) -C $(KERNEL_SRC) M=$(PWD) modules

clean:

              $(MAKE) -C $(KERNEL_SRC) M=$(PWD) clean

For external modules, NXP’s current i.MX Linux 6.12 guide says the requirements are a compiled kernel, a board running the same kernel version, and a toolchain; it also notes that a full kernel compilation is required to generate the headers and symbol files needed for external module compilation. The same guide uses the standard external-module form:

make -C $(KERNEL_SRC) M=$(PWD) modules

and then copies the resulting .ko to the board for insmod .

If you specifically want on-target builds, you can manually install a matching prepared kernel tree on the target, but treat it as a manual workaround rather than a documented i.MX8MP Flexbuild “install headers” feature:

# on target

sudo mkdir -p /usr/src/linux-headers-$(uname -r)

sudo ln -sfn /usr/src/linux-headers-$(uname -r) /lib/modules/$(uname -r)/build

Copy the matching Flexbuild kernel source/build artifacts from the host into that directory, including the generated files and Module.symvers . Then on the target:

cd /usr/src/linux-headers-$(uname -r)

make oldconfig

make prepare

# or, for module builds:

make modules_prepare

The important points are:

• The kernel source/build tree must match the exact kernel running on the board: check uname -r .
• Module.symvers should be present; otherwise module versioning/dependency information may be missing.
• make oldconfig && make prepare / make modules_prepare is the usual step to prepare the tree for external module builds.
• Native builds on the board are usually slower; NXP guidance generally recommends host-side cross-compilation for i.MX external modules.

So the short answer is: Flexbuild can build the matching kernel, but for i.MX8MP Debian I would build the module on the host against the Flexbuild kernel tree, not try to install distro-style linux-headers on the board. If you need on-target iteration, copy the matching prepared kernel tree to /usr/src/linux-headers-$(uname -r) and point /lib/modules/$(uname -r)/build at it.

Use the Flexbuild-compiled kernel tree as your “headers” source; a packaged, apt-installable linux-headers-$(uname -r) flow is not documented for i.MX8MP Flexbuild Debian in the material retrieved.