acquire_reference
id = acquire_reference(env, insn_idx);
int id = acquire_reference(env, insn_idx);
int id = acquire_reference(env, insn_idx);
static int acquire_reference(struct bpf_verifier_env *env, int insn_idx);
acquire_reference(env, 0) : 0;
id = acquire_reference(env, insn_idx);