Re: [for-linus][PATCH 01/10] tracing: Suppress sparse warnings triggered by is_signed_type()

[Rasmus Villemoes]

On 22/08/2022 20.45, Linus Torvalds wrote:
> On Mon, Aug 22, 2022 at 11:20 AM Bart Van Assche <bvanassche@xxxxxxx> wrote:
>>
>> I agree that it's better that sparse sees the same code as what is used to
>> build the kernel. However, I do not agree that the patch above is a solution.
>> Sparse reports a warning for the suggested definition above of is_signed_type()
>> because the new definition tries to use the less-than (<) operator to compare
>> two __bitwise types.
> 
> Argh. I forgot that part. It wasn't just the cast that warned, it was
> the compare too.
> 
> But we did have a sparse fix for it, didn't we? That fix required that
> the '< (type)1' cast be changed to '<= (type)0' iirc, and a patch to
> sparse, but it at least avoided the problem.

Heh. I originally wrote the comparison "< (t)1" instead of "< (t)0" to
avoid a -Wtype-limits warning when applied to unsigned types - yeah
yeah, the kernel isn't built with that, but it's a nice macro to
copy-paste to other projects, and sometimes people do explicitly enable
-Wtype-limits to manually go through some, and then it's nice to not
have tons of false positives from this macro.

But of course <1 is the same as <=0, and we can indeed spell it that way
without triggering Wtype-limits. So if that can help with also silencing
sparse, ack from me on that part.

Rasmus