Hi,
David Hildenbrand <david@xxxxxxxxxx> writes:
> On 29.11.21 15:21, Sven Schnelle wrote:
>> Yafang Shao <laoar.shao@xxxxxxxxx> writes:
>>> Thanks for the report and debugging!
>>> Seems we should explicitly define it as signed ?
>>> Could you pls. help verify it?
>>>
>>> diff --git a/include/linux/sched.h b/include/linux/sched.h
>>> index cecd4806edc6..44d36c6af3e1 100644
>>> --- a/include/linux/sched.h
>>> +++ b/include/linux/sched.h
>>> @@ -278,7 +278,7 @@ struct task_group;
>>> * Define the task command name length as enum, then it can be visible to
>>> * BPF programs.
>>> */
>>> -enum {
>>> +enum SignedEnum {
>>> TASK_COMM_LEN = 16,
>>> };
>>
>> Umm no. What you're doing here is to define the name of the enum as
>> 'SignedEnum'. This doesn't change the type. I think before C++0x you
>> couldn't force an enum type.
>
> I think there are only some "hacks" to modify the type with GCC. For
> example, with "__attribute__((packed))" we can instruct GCC to use the
> smallest type possible for the defined enum values.
Yes, i meant no way that the standard defines. You could force it to
signed by having a negative member.
> I think with some fake entries one can eventually instruct GCC to use an
> unsigned type in some cases:
>
> https://stackoverflow.com/questions/14635833/is-there-a-way-to-make-an-enum-unsigned-in-the-c90-standard-misra-c-2004-compl
>
> enum {
> TASK_COMM_LEN = 16,
> TASK_FORCE_UNSIGNED = 0x80000000,
> };
>
> Haven't tested it, though, and I'm not sure if we should really do that
> ... :)
TBH, i would vote for reverting the change. defining an array size as
enum feels really odd.
Regards
Sven
