From: j.anaszewski@samsung•com (Jacek Anaszewski)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH 00/38] Fixes related to incorrect usage of unsigned types
Date: Tue, 22 Sep 2015 11:46:58 +0200 [thread overview]
Message-ID: <56012392.7020807@samsung.com> (raw)
In-Reply-To: <56011BB9.5030004@samsung.com>
On 09/22/2015 11:13 AM, Andrzej Hajda wrote:
> On 09/21/2015 03:42 PM, David Howells wrote:
>> Andrzej Hajda <a.hajda-Sze3O3UU22JBDgjK7y7TUQ@public•gmane.org> wrote:
>>
>>> Semantic patch finds comparisons of types:
>>> unsigned < 0
>>> unsigned >= 0
>>> The former is always false, the latter is always true.
>>> Such comparisons are useless, so theoretically they could be
>>> safely removed, but their presence quite often indicates bugs.
>>
>> Or someone has left them in because they don't matter and there's the
>> possibility that the type being tested might be or become signed under some
>> circumstances. If the comparison is useless, I'd expect the compiler to just
>> discard it - for such cases your patch is pointless.
>>
>> If I have, for example:
>>
>> unsigned x;
>>
>> if (x == 0 || x > 27)
>> give_a_range_error();
>>
>> I will write this as:
>>
>> unsigned x;
>>
>> if (x <= 0 || x > 27)
>> give_a_range_error();
>>
>> because it that gives a way to handle x being changed to signed at some point
>> in the future for no cost. In which case, your changing the <= to an ==
>> "because the < part of the case is useless" is arguably wrong.
>
> This is why I have not checked for such cases - I have skipped checks of type
> unsigned <= 0
> exactly for the reasons above.
>
> However I have left two other checks as they seems to me more suspicious - they
> are always true or false. But as Dmitry and Andrew pointed out Linus have quite
> strong opinion against removing range checks in such cases as he finds it
> clearer. I think it applies to patches 29-36. I am not sure about patches 26-28,37.
Dropped 30/38 and 31/38 from LED tree then.
--
Best Regards,
Jacek Anaszewski
prev parent reply other threads:[~2015-09-22 9:46 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <1442842450-29769-1-git-send-email-a.hajda@samsung.com>
2015-09-21 13:33 ` [PATCH 13/38] ARM: shmobile: apmu: correct type of CPU id Andrzej Hajda
2015-10-02 1:57 ` Simon Horman
2015-09-21 13:42 ` [PATCH 00/38] Fixes related to incorrect usage of unsigned types David Howells
2015-09-22 9:13 ` Andrzej Hajda
2015-09-22 9:46 ` Jacek Anaszewski [this message]
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