sys-kernel/coreos-modules: arm64: Enable CONFIG_FUNCTION_TRACER & CONFIG_DYNAMIC_FTRACE

[tidusete]

kernel-arm64: Enable CONFIG_FUNCTION_TRACER

Currently, the function tracer is disabled on ARM64 builds, unlike x86 builds where it is standard. This prevents standard observability and security tools (like those using eBPF, ftrace, or security agents) from reading available_filter_functions and attaching probes, causing them to crash or fail to start.

This change enables CONFIG_FUNCTION_TRACER and CONFIG_DYNAMIC_FTRACE in the ARM64 kernel configuration. This provides feature parity with x86_64 builds and ensures support for the modern Linux tracing ecosystem on ARM64.

Fixes #1974

How to use

1. Build an ARM64 image with these changes (or wait for CI to generate one).
2. Boot the image (e.g., in QEMU on an ARM64 host or via image_to_vm.sh).
3. Verify that the kernel configuration contains the new flags: zgrep FTRACE /proc/config.gz

Testing done

Booted the built image in QEMU (ARM64) and verified the configuration and availability of tracing functions.

core@localhost ~ $ zgrep CONFIG_FUNCTION_TRACER /proc/config.gz
CONFIG_FUNCTION_TRACER=y

core@localhost ~ $ zgrep CONFIG_DYNAMIC_FTRACE /proc/config.gz
CONFIG_DYNAMIC_FTRACE=y

core@localhost ~ $ ls -l /sys/kernel/tracing/available_filter_functions
-r--r--r-- 1 root root 0 Feb  3 15:22 /sys/kernel/tracing/available_filter_functions

CI 🟢 : http://localhost:8080/job/container/job/packages_all_arches/7368/cldsv/

[jepio]

@tidusete thank you - this makes sense as we often make changes to align the kernel configs between arches. Would you mind moving the entries to the common_defconfig though?

[tormath1]

Thanks, it looks good. Might I ask you to add a changelog entry as well into changelog/changes/ ?

[tidusete]

I think it should be good now :)

[tormath1]

Thanks a lot @tidusete for the contribution. As this is an observability feature and it's already around for amd64, I'll backport this to current Alpha, Beta and Stable.

EDIT: Backported to:

• flatcar-4593
• flatcar-4547
• flatcar-4459

[tidusete]

Thanks for the backports @tormath1!

Just for clarification regarding flatcar-4459: does this mean the changes are queued for the next patch release of that series (e.g., 4459.2.4), or are they available immediately?

Knowing the target patch version would help us track exactly when we can deploy the fix to our nodes

[tormath1]

Thanks for the backports @tormath1!

Just for clarification regarding flatcar-4459: does this mean the changes are queued for the next patch release of that series (e.g., 4459.2.4), or are they available immediately?

Knowing the target patch version would help us track exactly when we can deploy the fix to our nodes

Hey, we're currently discussing about promoting current Beta to Stable - so next release Stable will be 4547.2.0 and will hold this change.

If the promotion does not append, the next stable will be 4547.2.4 and will hold the fix as well. :)

[tormath1]

Hey @tidusete I have some bad news for this patch. We had to revert it on flatcar-4459 (current Stable) - as it was increasing too much the /boot partition size for ARM64 builds and this could create potential issues for next updates.

Alpha and Beta are not affected by this because we increased the size of the /boot partition, so you will have to wait for the next Beta->Stable promotion (which should append next month) to see this feature enabled.