linux-kernel - Re: [patch 3/6] futex: Get rid of the val2 conditional dance

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Date:   Fri, 23 Apr 2021 20:21:58 -0300
From:   André Almeida <andrealmeid@...labora.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Adhemerval Zanella <adhemerval.zanella@...aro.org>,
        Lukasz Majewski <lukma@...x.de>,
        Florian Weimer <fweimer@...hat.com>,
        Carlos O'Donell <carlos@...hat.com>,
        "Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>,
        Davidlohr Bueso <dave@...olabs.net>,
        Ingo Molnar <mingo@...nel.org>,
        Darren Hart <dvhart@...radead.org>,
        Andrei Vagin <avagin@...il.com>,
        Kurt Kanzenbach <kurt@...utronix.de>, kernel@...labora.com
Subject: Re: [patch 3/6] futex: Get rid of the val2 conditional dance

Às 19:34 de 23/04/21, Thomas Gleixner escreveu:
> On Fri, Apr 23 2021 at 18:40, André Almeida wrote:
>>>    
>>> -	return do_futex(uaddr, op, val, tp, uaddr2, val2, val3);
>>> +	return do_futex(uaddr, op, val, tp, uaddr2, (unsigned long)utime, val3);
>>
>> Given do_futex()'s type signature, I think it makes more sense to cast
>> utime to u32.
> 
> It's a pointer which you better force cast to unsigned long first.
> 
> So the explicit thing would be '(u32)(unsigned long) utime' which is
> what the val2 dance stupidly did with 'int'
> 
> 		val2 = (int) (unsigned long) utime;
> 
> But with doing it at function call argument it's implicit, because the
> 
>    unsigned long  to u32 conversion is well defined
> 
> while
> 
>    (u32)ptr
> 
> is only well defined on 32bit.
> 

I see, thank you for the clarification!

> Thanks,
> 
>          tglx
>