How to get access to hit/miss kprobe stat while using pmuKprobe

[nloginov]

Hello, community of cilium/ebpf!

Previously I used https://github.com/iovisor/gobpf library, and that library created kprobe through tracefs, so that I was able to monitor statistic about total count of hit and miss kprobes through /sys/kernel/debug/tracing/kprobe_profile file.

I found out that by default cillium/ebpf is creating kprobes using PMU, and it falls back to the tracefs only if PMU method is not supported:

ebpf/link/kprobe.go

Lines 184 to 199 in aaa9af2

	tp, err := pmuKprobe(args)
	if errors.Is(err, os.ErrNotExist) || errors.Is(err, unix.EINVAL) {
	args.symbol = platformPrefix(symbol)
	tp, err = pmuKprobe(args)
	}
	if err == nil {
	return tp, nil
	}
	if err != nil && !errors.Is(err, ErrNotSupported) {
	return nil, fmt.Errorf("creating perf_kprobe PMU: %w", err)
	}
	// Use tracefs if kprobe PMU is missing.
	args.symbol = symbol
	tp, err = tracefsKprobe(args)
	if errors.Is(err, os.ErrNotExist) || errors.Is(err, unix.EINVAL) {

I assume that it is a more modern and proper way of creating kprobe, but could you tell me how I can access to the hit/miss statistic using this approach?

Let's say my ebpf program crashed during execution (e.g. referenced invalid memory address): with tracefs method this failed execution will fall under "miss" counter in /sys/kernel/debug/tracing/kprobe_profile file, and I will be able to monitor that. With PMU method no such file is created and I have no idea where I can get this information or is it possible at all, could you help me? Thanks in advance!

[lmb]

That's a fair question. As far as I know the kernel currently doesn't expose that kind of information, see #755 (comment)

(Thanks to @mmat11 for digging up the necessary information).

[mmat11]

From this message #755 (comment) I understand it's not currently possible