btf_get_from_fd
btf = btf_get_from_fd(btf_fd, base_btf);
btf = btf_get_from_fd(fd, obj->btf_vmlinux);
struct btf *btf_get_from_fd(int btf_fd, struct btf *base_btf);
mod_btf = btf_get_from_fd(btf_fd[1], vmlinux_btf);