I checked with Will about it and learnt that ARM64 does support
patching certain instructions (e.g. branch, brk, nops) using
aarch64_insn_patch_text_nosync, it's used in ftrace:

https://elixir.bootlin.com/linux/latest/source/arch/arm64/kernel/ftrace.c#L24

But one has to tolerate that not all CPUs will execute these
instructions until a context synchronization happens due to an
exception or an ISB instruction. But I think we can start
with the same thing that FTrace does?

- KP

On Wed, Feb 24, 2021 at 10:01 PM Daniel Borkmann [off-list ref] wrote:

On 2/24/21 8:54 PM, Luigi Rizzo wrote:

quoted

I prepared a BPF version of kstats[1]
https://github.com/luigirizzo/lr-cstats
that uses fentry/fexit hooks to monitor the execution time
of a kernel function.

I hoped to have it working on ARM64 too, but it looks like
arch_prepare_bpf_trampoline() only exists for x86.

Is there any outstanding patch for this function on ARM64,
or any similar function I could look at to implement it myself ?

Not that I'm currently aware of, arm64 support would definitely be great
to have. From x86 side, the underlying arch dependency was basically on
text_poke_bp() to patch instructions on a live kernel. Haven't checked
recently whether an equivalent exists on arm64 yet, but perhaps Will
might know.

quoted

[1] kstats is an in-kernel also in the above repo and previously
discussed at https://lwn.net/Articles/813303/