sudo apt-get install libelf-dev
git clone --depth 1 https://github.com/libbpf/libbpf
cd libbpf/src
sudo make install

sudo apt install clang-11 --install-suggests

sudo apt install llvm

hello_packet_func.bpf.o:        file format ELF64-BPF

Disassembly of section xdp:
hello:
; int hello(struct xdp_md *ctx) {
       0:       18 06 00 00 00 00 00 00 00 00 00 00 00 00 00 00         r6 = 0 ll
; bpf_printk("Hello World %d", counter);
       2:       61 63 00 00 00 00 00 00         r3 = *(u32 *)(r6 + 0)
       3:       18 01 00 00 00 00 00 00 00 00 00 00 00 00 00 00         r1 = 0 ll
       5:       b7 02 00 00 0f 00 00 00         r2 = 15
       6:       85 00 00 00 06 00 00 00         call 6
; counter++;
       7:       61 61 00 00 00 00 00 00         r1 = *(u32 *)(r6 + 0)
       8:       07 01 00 00 01 00 00 00         r1 += 1
       9:       63 16 00 00 00 00 00 00         *(u32 *)(r6 + 0) = r1
; return XDP_PASS;
      10:       b7 00 00 00 02 00 00 00         r0 = 2
      11:       95 00 00 00 00 00 00 00         exit