Return-path: Received: from mailout4.w1.samsung.com ([210.118.77.14]:16388 "EHLO mailout4.w1.samsung.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753339AbbIVJrF (ORCPT ); Tue, 22 Sep 2015 05:47:05 -0400 Message-id: <56012392.7020807@samsung.com> (sfid-20150922_114754_136889_7AF1E58D) Date: Tue, 22 Sep 2015 11:46:58 +0200 From: Jacek Anaszewski MIME-version: 1.0 To: Andrzej Hajda Cc: David Howells , Bartlomiej Zolnierkiewicz , Marek Szyprowski , linux-kernel@vger.kernel.org, brcm80211-dev-list@broadcom.com, devel@driverdev.osuosl.org, dev@openvswitch.org, dri-devel@lists.freedesktop.org, intel-gfx@lists.freedesktop.org, linux-api@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-cachefs@redhat.com, linux-clk@vger.kernel.org, linux-crypto@vger.kernel.org, linux-fbdev@vger.kernel.org, linux-input@vger.kernel.org, linux-leds@vger.kernel.org, linux-media@vger.kernel.org, linux-mips@linux-mips.org, linux-mm@kvack.org, linux-omap@vger.kernel.org, linux-rdma@vger.kernel.org, linux-serial@vger.kernel.org, linux-sh@vger.kernel.org, linux-usb@vger.kernel.org, linux-wireless@vger.kernel.org, lustre-devel@lists.lustre.org, netdev@vger.kernel.org, rtc-linux@googlegroups.com Subject: Re: [PATCH 00/38] Fixes related to incorrect usage of unsigned types References: <1442842450-29769-1-git-send-email-a.hajda@samsung.com> <17571.1442842945@warthog.procyon.org.uk> <56011BB9.5030004@samsung.com> In-reply-to: <56011BB9.5030004@samsung.com> Content-type: text/plain; charset=windows-1252; format=flowed Sender: linux-wireless-owner@vger.kernel.org List-ID: On 09/22/2015 11:13 AM, Andrzej Hajda wrote: > On 09/21/2015 03:42 PM, David Howells wrote: >> Andrzej Hajda 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