linux-kernel - Re: [for-linus][PATCH 01/10] tracing: Suppress sparse warnings triggered by is_signed

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Message-ID: <353e5bbd-cdd1-f818-6a2f-9a7c800f9879@acm.org>
Date:   Wed, 24 Aug 2022 16:28:25 -0700
From:   Bart Van Assche <bvanassche@....org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Rasmus Villemoes <linux@...musvillemoes.dk>,
        Steven Rostedt <rostedt@...dmis.org>,
        linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Christoph Hellwig <hch@....de>,
        Luc Van Oostenryck <luc.vanoostenryck@...il.com>,
        Jens Axboe <axboe@...nel.dk>
Subject: Re: [for-linus][PATCH 01/10] tracing: Suppress sparse warnings
 triggered by is_signed_type()

On 8/23/22 18:49, Linus Torvalds wrote:
> On Tue, Aug 23, 2022 at 5:09 PM Bart Van Assche <bvanassche@....org> wrote:
>>
>> I'm probably doing something wrong but even with sparse commit 658ee8e0f631
>> ("unrestricted values are unrestricted even after a cast") I see warnings
>> being triggered by users of the is_signed_type() macro, warnings that
>> disappear if I change the definition of the is_signed_type() macro into 0:
> 
> That's the
> 
>> It does require that kernel change to make
>>
>>    #define is_signed_type(type)   (((type)(-1)) <= (type)0)
> 
> part I was talking about.
> 
> So your kernel side patch looks fine, except I don't think you need
> the '__force' - the sparse patches in my tree should make sparse happy
> about casting '-1'.
> 
> But I didn't do very much testing.

Hi Linus,

Can you take a look at the following report from the kernel test robot:
https://lore.kernel.org/all/202208250433.EVz5pZkB-lkp@intel.com/ ?

Do I see correctly that gcc reports a new warning for the above 
definition of is_signed_type() with W=1? I'm not sure how to get rid of 
that new gcc warning without reintroducing a sparse warning.

The tree that the kernel robot tested is available here: 
https://github.com/bvanassche/linux/tree/tracing

Thanks,

Bart.