BPF program using XDP returns failed to load BPF skeleton (-22) - ebpf

Question

Firstly, I was not using the libbpf API directly, neither BCC. Instead, I was trying to use the API of the skeleton generated by bpftool.
Control code:
obj_gen = bpf_xdp_c__open();
if (!obj_gen)
goto cleanup;
ifindex = if_nametoindex("eth0");
if(!ifindex)
{
perror("if_nametoindex");
return 1;
}
err = bpf_xdp_c__load(obj_gen);
BPF code:
// Simple XDP BPF program. Everything packet will be dropped.
SEC("test")
int xdp_prog1(struct xdp_md *ctx){
char drop_message[] = "XDP PACKET DROP\n";
bpf_trace_printk(&drop_message, sizeof(drop_message));
return XDP_DROP;
}
So, after running, the error below was shown:
// libbpf: load bpf program failed: Invalid argument
// libbpf: failed to load program 'test'
// libbpf: failed to load object 'bpf_xdp_c'
// libbpf: failed to load BPF skeleton 'bpf_xdp_c': -22
After debugging, I have noticed that the program type was not with the correct value. It was always returning 0. So, I had to define the following code before the load call:
obj_gen->progs.xdp_prog1->type = BPF_PROG_TYPE_XDP;
Because the struct bpf_program was in the libbpf.c, I had to redefine in my header in in order to the compile find it. This workaround worked.
Q: Is there a better solution?

Answer 1

I found what it was wrong. After looking at libbpf source coude, I found the variable
static const struct bpf_sec_def section_defs[] = {... BPF_PROG_SEC("xdp",BPF_PROG_TYPE_XDP), ...
So, I noticed that I have not defined my XDP section in my BPF program with SEC("xdp").
Thanks #Qeole for your help.