Re: [PATCH bpf-next v5 7/9] selftests/bpf: Test kptr arrays and kptrs in nested struct fields.

[Kui-Feng Lee <sinquersw@gmail.com>]

On 5/10/24 16:29, Eduard Zingerman wrote:
> On Fri, 2024-05-10 at 16:17 -0700, Eduard Zingerman wrote:
>> On Fri, 2024-05-10 at 16:04 -0700, Kui-Feng Lee wrote:
>>
>> [...]
>>
>>
>>> I am not sure if I read you question correctly.
>>>
>>> For example, we have 3 correct info.
>>>
>>>    [info(offset=0x8), info(offset=0x10), info(offset=0x18)]
>>>
>>> And We have program that includes 3 instructions to access the offset
>>> 0x8, 0x10, and 0x18. (let's assume these load instructions would be
>>> checked against infos)
>>>
>>>    load r1, [0x8]
>>>    load r1, [0x10]
>>>    load r1, [0x18]
>>>
>>> If everything works as expected, the verifier would accept the program.
>>>
>>> Otherwise, like you said, all 3 info are pointing to the same offset.
>>>
>>>    [info(0offset=0x8), info(offset=0x8), info(offset=0x8)]
>>>
>>> Then, the later two instructions should fail the check.
> 
> Ok, what you are saying is possible not with load but with some kfunc
> that accepts a special pointer. E.g. when verifier.c:check_kfunc_args()
> expects an argument of KF_ARG_PTR_TO_LIST_HEAD type it would report an
> error if special field is not found.
> 
> So the structure of the test would be:
> - define a nested data structure with list head at some leafs;
> - in the BPF program call a kfunc accessing each of the list heads;
> - if all offsets are computed correctly there would be no load time error;
> - this is a load time test, no need to actually run the BPF program.
> 
> [...]

Yes, that is what I meant.
Sorry for replying late.