optimize: fallback to syscall if failed to detect kernel version

pkg/ebpf_internal/version.go

@@ -1,10 +1,11 @@
-// Copied from https://github.com/cilium/ebpf/blob/v0.10.0/internal/version.go
+// Modified from https://github.com/cilium/ebpf/blob/v0.10.0/internal/version.go
 
 package internal
 
 import (
 	"fmt"
 	"sync"
+	"syscall"
 
 	"github.com/v2rayA/dae/pkg/ebpf_internal/internal/unix"
 )
@@ -89,10 +90,34 @@ func (v Version) Kernel() uint32 {
 	return uint32(uint8(v[0]))<<16 | uint32(uint8(v[1]))<<8 | uint32(uint8(s))
 }
 
+// utsnameToString converts the utsname to a string and returns it.
+func utsnameToString(unameArray [65]int8) string {
+	var byteString [65]byte
+	var indexLength int
+	for ; unameArray[indexLength] != 0; indexLength++ {
+		byteString[indexLength] = uint8(unameArray[indexLength])
+	}
+	return string(byteString[:indexLength])
+}
+
 // KernelVersion returns the version of the currently running kernel.
 func KernelVersion() (Version, error) {
 	kernelVersion.once.Do(func() {
 		kernelVersion.version, kernelVersion.err = detectKernelVersion()
+		if kernelVersion.err != nil {
+			// Try syscall.
+			var utsname syscall.Utsname
+			if err := syscall.Uname(&utsname); err != nil {
+				kernelVersion.err = fmt.Errorf("%w; %v", kernelVersion.err, err)
+				return
+			}
+			version, err := NewVersion(utsnameToString(utsname.Release))
+			if err != nil {
+				kernelVersion.err = fmt.Errorf("%w; %v", kernelVersion.err, err)
+				return
+			}
+			kernelVersion.version = version
+		}
 	})
 
 	if kernelVersion.err != nil {