btf__add_var
LIBBPF_API int btf__add_var(struct btf *btf, const char *name, int linkage, int type_id);
dummy_var_btf_id = btf__add_var(btf,
var_id = btf__add_var(btf, "some_var", BTF_VAR_GLOBAL_ALLOCATED, 1);
btf__add_var(btf, "var1", BTF_VAR_STATIC, 1); /* [15] static int var1; */
btf__add_var(btf, "var2", BTF_VAR_STATIC, 3); /* [16] static int *var2; */
id = btf__add_var(btf, "var1", BTF_VAR_GLOBAL_ALLOCATED, 1);