code: func loadSimpleBpf(progType BpfProgType, ret uint32) (int, error) {
  	insns := []uint64{
  		0x00000000000000b7 | (uint64(ret) << 32),
  		0x0000000000000095,
  	}
  	license := []byte{'A', 'S', 'L', '2', '\x00'}
  	attr := BPFAttr{
  		ProgType: uint32(progType),
  		InsnCnt:  uint32(len(insns)),
  		Insns:    uintptr(unsafe.Pointer(&insns[0])),
  		License:  uintptr(unsafe.Pointer(&license[0])),
  	}
  	fd, _, errno := unix.Syscall(unix.SYS_BPF,
  		5, /* bpf cmd */
  		uintptr(unsafe.Pointer(&attr)),
  		unsafe.Sizeof(attr))
  	if errno != 0 {
  		return 0, errno
  	}
  	return int(fd), nil
  }
docs: // loadSimpleBpf loads a trivial bpf program for testing purposes.