Describe the bug

When trying to attach an eBPF program to a tracepoint whose group contains a hyphen (e.g. xhci-hcd), link.Tracepoint fails with:

opening tracepoint: invalid tracefs group: "xhci-hcd"

This happens because the validIdentifier function currently rejects hyphens (-), even though they are valid in tracefs event groups (for example, USB tracepoints use xhci-hcd).
This prevents attaching to valid tracepoints that exist in the kernel.

Expected behavior

The tracepoint should attach successfully, since xhci-hcd is a valid group under /sys/kernel/tracing/events/.

How to reproduce

Build a simple Go program that tries to attach to a tracepoint with a - in the group:

tp, err := link.Tracepoint("xhci-hcd", "xhci_setup_device", objs.XhciSetupDevice, nil)
if err != nil {
	log.Fatalf("opening tracepoint: %s", err)
}
defer tp.Close()

and run the program.

Version information

github.com/cilium/ebpf v0.19.0