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

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Message-ID: <29157fcb-a2c3-ff4d-2b74-f4da860a0dbe@rasmusvillemoes.dk>
Date:   Thu, 25 Aug 2022 09:57:25 +0200
From:   Rasmus Villemoes <linux@...musvillemoes.dk>
To:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Bart Van Assche <bvanassche@....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 25/08/2022 02.40, Linus Torvalds wrote:
> On Wed, Aug 24, 2022 at 5:30 PM Linus Torvalds
> <torvalds@...ux-foundation.org> wrote:
>>
>> Let me think about this.
> 
> Actually, thinking about it, that was simple enough.
> 
>   -#define is_signed_type(type)   (((type)(-1)) < (type)1)
>   +#define is_signed_type(type)   (((type)(-1)) < (__force type)1)
> 
> should work.
> 
> It looks a bit odd, because we only force one side.

One can also make the RHS not be a null pointer constant with something like

(((t)(-1)) <= (1 ? (t)0 : (t)0))

In either case, we're a good way into "this needs a comment explaining
why it's written precisely the way it is" territory.

Rasmus