From: Andrzej Hajda <a.hajda@samsung•com>
To: David Howells <dhowells@redhat•com>
Cc: linux-mips@linux-mips•org, linux-fbdev@vger•kernel.org,
linux-sh@vger•kernel.org, brcm80211-dev-list@broadcom•com,
dri-devel@lists•freedesktop.org, linux-mm@kvack•org,
linux-clk@vger•kernel.org, linux-leds@vger•kernel.org,
Marek Szyprowski <m.szyprowski@samsung•com>,
devel@driverdev•osuosl.org, linux-rdma@vger•kernel.org,
linux-cachefs@redhat•com, linux-serial@vger•kernel.org,
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dev@openvswitch•org, rtc-linux@googlegroups•com,
Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung•com>,
intel-gfx@lists•freedesktop.org, linux-omap@vger•kernel.org,
linux-arm-kernel@lists•infradead.org,
Andrzej Hajda <a.hajda@samsung•com>,
linux-api@vger•kernel.org, linux-usb@vger•kernel.org,
linux-wireless@vger•kernel.org, linux-kernel@vger•kernel.org,
linux-crypto@vger•kernel.org, netdev@vger•kernel.org,
lustre-devel@lists•lustre.org
Subject: Re: [PATCH 00/38] Fixes related to incorrect usage of unsigned types
Date: Tue, 22 Sep 2015 11:13:29 +0200 [thread overview]
Message-ID: <56011BB9.5030004@samsung.com> (raw)
In-Reply-To: <17571.1442842945@warthog.procyon.org.uk>
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.
Regards
Andrzej
>
> David
> --
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next prev parent reply other threads:[~2015-09-22 9:13 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-09-21 13:33 [PATCH 00/38] Fixes related to incorrect usage of unsigned types Andrzej Hajda
[not found] ` <1442842450-29769-1-git-send-email-a.hajda-Sze3O3UU22JBDgjK7y7TUQ@public.gmane.org>
2015-09-21 13:33 ` [PATCH 08/38] openvswitch: fix handling result of ipv6_skip_exthdr Andrzej Hajda
2015-09-21 17:45 ` Pravin Shelar
2015-09-21 13:33 ` [PATCH 17/38] isdn: hisax: fix frame calculation Andrzej Hajda
2015-09-22 23:15 ` David Miller
2015-09-21 13:33 ` [PATCH 18/38] net/ibm/emac: fix type of phy_mode Andrzej Hajda
2015-09-22 23:14 ` David Miller
2015-09-21 13:33 ` [PATCH 19/38] net: stmmac: fix type of entry variable Andrzej Hajda
2015-09-22 23:15 ` David Miller
2015-09-21 13:33 ` [PATCH 20/38] net: brcm80211: fix range check Andrzej Hajda
2015-09-22 23:15 ` David Miller
2015-09-21 13:33 ` [PATCH 21/38] mwifiex: fix comparison expression Andrzej Hajda
2015-09-22 10:56 ` Amitkumar Karwar
2015-09-22 23:15 ` David Miller
2015-09-21 13:33 ` [PATCH 22/38] orinoco: fix checking for default value Andrzej Hajda
2015-09-22 23:15 ` David Miller
2015-09-21 13:33 ` [PATCH 23/38] rndis_wlan: " Andrzej Hajda
2015-09-22 23:15 ` David Miller
2015-09-21 13:33 ` [PATCH 27/38] usbnet: remove invalid check Andrzej Hajda
2015-09-22 23:15 ` David Miller
[not found] ` <17571.1442842945@warthog.procyon.org.uk>
2015-09-22 9:13 ` Andrzej Hajda [this message]
2015-09-22 9:46 ` [PATCH 00/38] Fixes related to incorrect usage of unsigned types Jacek Anaszewski
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