Re: [PATCH bpf-next v7 08/11] selftests/bpf: Add tests to verify global percpu data

[Leon Hwang <leon.hwang@linux.dev>]

On 22/6/26 22:57, sashiko-bot@kernel.org wrote:
[...]
>> diff --git a/tools/testing/selftests/bpf/prog_tests/global_percpu_subskel.c b/tools/testing/selftests/bpf/prog_tests/global_percpu_subskel.c
>> new file mode 100644
>> index 0000000000000..8aebd533d86b5
>> --- /dev/null
>> +++ b/tools/testing/selftests/bpf/prog_tests/global_percpu_subskel.c
> [ ... ]
>> +void test_global_percpu_data_subskel(void)
>> +{
>> +	struct test_global_percpu_data *subskel = NULL;
>> +	struct bpf_object *obj;
>> +	int i;
> [ ... ]
>> +	if (!ASSERT_OK_PTR(subskel->subskel, "subskel"))
>> +		goto out;
>> +	if (!ASSERT_OK_PTR(subskel->maps.percpu, "maps.percpu"))
>> +		goto out;
>> +	ASSERT_EQ(bpf_map__type(subskel->maps.percpu), BPF_MAP_TYPE_PERCPU_ARRAY,
>> +		  "percpu_map_type");
>> +	ASSERT_GT(subskel->subskel->var_cnt, 0, "var_cnt");
> 
> [Severity: Medium]
> Will this assertion cause the test to unconditionally fail?
> 

Luckily, no.

> Looking at test_global_percpu_data.c, all defined variables are placed
> in the .percpu section. Since bpftool explicitly skips .percpu maps when
> generating subskeletons, there appear to be no non-percpu maps with BTF
> variables present.
> 
> If that is the case, subskel->subskel->var_cnt will be exactly 0, causing
> this check to evaluate to ASSERT_GT(0, 0) and reliably fail the test.
> 

Looking at test_global_percpu_data.c, there are 5 non-percpu global
variables, which were added in patch #11.

volatile const __u32 num_cpus = 0;
volatile const int offsetof_num;
volatile const int elem_sz;
__u32 percpu_data_sum = 0;
bool run_iter = false;

So, subskel->subskel->var_cnt will be 5.

In the generated test_global_percpu_data.subskel.h:
        /* vars */
        s->var_cnt = 5;


Thanks,
Leon

>> +
>> +	for (i = 0; i < subskel->subskel->var_cnt; i++) {
>> +		const struct bpf_var_skeleton *var;
> [ ... ]
>