From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f42.google.com (mail-pa0-f42.google.com [209.85.220.42]) by kanga.kvack.org (Postfix) with ESMTP id 3A2166B0038 for ; Tue, 22 Sep 2015 05:13:57 -0400 (EDT) Received: by pacex6 with SMTP id ex6so4250198pac.0 for ; Tue, 22 Sep 2015 02:13:57 -0700 (PDT) Received: from mailout4.w1.samsung.com (mailout4.w1.samsung.com. [210.118.77.14]) by mx.google.com with ESMTPS id r3si1075444pap.0.2015.09.22.02.13.56 for (version=TLSv1 cipher=RC4-SHA bits=128/128); Tue, 22 Sep 2015 02:13:56 -0700 (PDT) Received: from eucpsbgm1.samsung.com (unknown [203.254.199.244]) by mailout4.w1.samsung.com (Oracle Communications Messaging Server 7.0.5.31.0 64bit (built May 5 2014)) with ESMTP id <0NV200D60MZ4DV70@mailout4.w1.samsung.com> for linux-mm@kvack.org; Tue, 22 Sep 2015 10:13:52 +0100 (BST) 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> From: Andrzej Hajda Message-id: <56011BB9.5030004@samsung.com> Date: Tue, 22 Sep 2015 11:13:29 +0200 MIME-version: 1.0 In-reply-to: <17571.1442842945@warthog.procyon.org.uk> Content-type: text/plain; charset=windows-1252 Content-transfer-encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: David Howells Cc: Andrzej Hajda , 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.orglinux-kernel@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 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. Regards Andrzej > > David > -- > To unsubscribe from this list: send the line "unsubscribe linux-wireless" in > the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org