Temporarily fix loading err on >= 6.6 kernels

[1] changed the kprobe loading behavior in a way that if we try to
attach a kprobe to a function with a duplicate name, then it will fail
with EADDRNOTAVAIL [2].

As pwru loads kprobes by using function symbol names, we are prone to
this behavior change.

Fix the loading problem by ignoring EADDRNOTAVAIL w/ the kprobe backend.
Also, instruct users when the kprobe.multi backend is used.

The proper fix is to use function addrs instead of syms when loading.
This is what Leon H. is working on.

[1]: https://lore.kernel.org/all/[email protected]/.
[2]: https://elixir.bootlin.com/linux/v6.6/source/kernel/trace/trace_kprobe.c#L884

Signed-off-by: Leon Hwang <[email protected]>
Signed-off-by: Martynas Pumputis <[email protected]>

main.go

@@ -298,7 +298,7 @@ func main() {
 				kp, err := link.Kprobe(name, fn, nil)
 				bar.Increment()
 				if err != nil {
-					if !errors.Is(err, os.ErrNotExist) {
+					if !errors.Is(err, os.ErrNotExist) && !errors.Is(err, syscall.EADDRNOTAVAIL) {
 						log.Fatalf("Opening kprobe %s: %s\n", name, err)
 					} else {
 						ignored += 1
@@ -319,6 +319,10 @@ func main() {
 			kp, err := link.KprobeMulti(fn, opts)
 			bar.Add(len(fns))
 			if err != nil {
+				if errors.Is(err, syscall.EADDRNOTAVAIL) {
+					log.Fatalf("Found duplicate function name in the kernel (%s). Set --backend=kprobe to fix the loading error until https://github.com/cilium/pwru/issues/284 has been fixed",
+						err)
+				}
 				log.Fatalf("Opening kprobe-multi for pos %d: %s\n", pos, err)
 			}
 			kprobes = append(kprobes, kp)