From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752456AbeDSEwD (ORCPT ); Thu, 19 Apr 2018 00:52:03 -0400 Received: from smtprelay0015.hostedemail.com ([216.40.44.15]:60339 "EHLO smtprelay.hostedemail.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1750913AbeDSEwB (ORCPT ); Thu, 19 Apr 2018 00:52:01 -0400 X-Session-Marker: 6A6F6540706572636865732E636F6D X-Spam-Summary: 2,0,0,,d41d8cd98f00b204,joe@perches.com,:::::::::::::::::::::::::::::,RULES_HIT:41:355:379:541:599:800:967:973:982:988:989:1260:1277:1311:1313:1314:1345:1359:1437:1515:1516:1518:1535:1542:1593:1594:1605:1711:1730:1747:1777:1792:2198:2199:2393:2525:2553:2559:2563:2682:2685:2689:2692:2693:2731:2828:2859:2933:2937:2939:2942:2945:2947:2951:2954:3022:3138:3139:3140:3141:3142:3622:3865:3866:3867:3868:3870:3871:3872:3873:3874:3934:3936:3938:3941:3944:3947:3950:3953:3956:3959:4321:4605:5007:6119:6691:6742:7903:8603:9025:10004:10400:10848:11232:11658:11914:12043:12295:12555:12663:12740:12760:12895:13141:13230:13255:13439:13618:14096:14097:14180:14181:14659:14721:14802:21060:21080:21324:21326:21451:21620:30012:30034:30054:30060:30070:30090:30091,0,RBL:72.2.237.46:@perches.com:.lbl8.mailshell.net-62.8.0.100 64.201.201.201,CacheIP:none,Bayesian:0.5,0.5,0.5,Netcheck:none,DomainCache:0,MSF:not bulk,SPF:fn,MSBL:0,DNSBL:neutral,Custom_rules:0:0:0,LFtime:20,LUA_SUMMARY:none X-HE-Tag: knot04_48ff0a3a3aa38 X-Filterd-Recvd-Size: 5218 Message-ID: Subject: Re: [PATCH] checkpatch: Add a --strict test for structs with bool member definitions From: Joe Perches To: Julia Lawall Cc: yuankuiz@codeaurora.org, Andrew Morton , Peter Zijlstra , "Rafael J. Wysocki" , Andy Whitcroft , Linux PM , "Rafael J. Wysocki" , Frederic Weisbecker , Thomas Gleixner , paulmck@linux.vnet.ibm.com, Ingo Molnar , Len Brown , Linux Kernel Mailing List , linux-pm-owner@vger.kernel.org Date: Wed, 18 Apr 2018 21:51:26 -0700 In-Reply-To: References: <891d4f632fbff5052e11f2d0b6fac35d@codeaurora.org> <20180410123305.GF4082@hirez.programming.kicks-ass.net> <95477c93db187bab6da8a8ba7c57836868446179.camel@perches.com> <20180410143950.4b8526073b4e3e34689f68cb@linux-foundation.org> <20180410150011.df9e036f57b5bcac7ac19686@linux-foundation.org> <20180411081502.GJ4082@hirez.programming.kicks-ass.net> <20180411092959.e666ec443e4d3bb6f43901d7@linux-foundation.org> <1c9f185f6086e9d89659f93720a27b660ee17c13.camel@perches.com> <5341b3b1945c4c1dbf7b356b1a7a4bd6ce304287.camel@perches.com> Content-Type: text/plain; charset="ISO-8859-1" X-Mailer: Evolution 3.28.1-2 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 2018-04-19 at 06:40 +0200, Julia Lawall wrote: > > On Wed, 18 Apr 2018, Joe Perches wrote: > > > On Tue, 2018-04-17 at 17:07 +0800, yuankuiz@codeaurora.org wrote: > > > Hi julia, > > > > > > On 2018-04-15 05:19 AM, Julia Lawall wrote: > > > > On Wed, 11 Apr 2018, Joe Perches wrote: > > > > > > > > > On Thu, 2018-04-12 at 08:22 +0200, Julia Lawall wrote: > > > > > > On Wed, 11 Apr 2018, Joe Perches wrote: > > > > > > > On Wed, 2018-04-11 at 09:29 -0700, Andrew Morton wrote: > > > > > > > > We already have some 500 bools-in-structs > > > > > > > > > > > > > > I got at least triple that only in include/ > > > > > > > so I expect there are at probably an order > > > > > > > of magnitude more than 500 in the kernel. > > > > > > > > > > > > > > I suppose some cocci script could count the > > > > > > > actual number of instances. A regex can not. > > > > > > > > > > > > I got 12667. > > > > > > > > > > Could you please post the cocci script? > > > > > > > > > > > I'm not sure to understand the issue. Will using a bitfield help if there > > > > > > are no other bitfields in the structure? > > > > > > > > > > IMO, not really. > > > > > > > > > > The primary issue is described by Linus here: > > > > > https://lkml.org/lkml/2017/11/21/384 > > > > > > > > > > I personally do not find a significant issue with > > > > > uncontrolled sizes of bool in kernel structs as > > > > > all of the kernel structs are transitory and not > > > > > written out to storage. > > > > > > > > > > I suppose bool bitfields are also OK, but for the > > > > > RMW required. > > > > > > > > > > Using unsigned int :1 bitfield instead of bool :1 > > > > > has the negative of truncation so that the uint > > > > > has to be set with !! instead of a simple assign. > > > > > > > > At least with gcc 5.4.0, a number of structures become larger with > > > > unsigned int :1. bool:1 seems to mostly solve this problem. The > > > > structure > > > > ichx_desc, defined in drivers/gpio/gpio-ich.c seems to become larger > > > > with > > > > both approaches. > > > > > > [ZJ] Hopefully, this could make it better in your environment. > > > IMHO, this is just for double check. > > > > I doubt this is actually better or smaller code. > > > > Check the actual object code using objdump and the > > struct alignment using pahole. > > I didn't have a chance to try it, but it looks quite likely to result in a > smaller data structure based on the other examples that I looked at. I _really_ doubt there is any difference in size between the below in any architecture struct foo { int bar; bool baz:1; int qux; }; and struct foo { int bar; bool baz; int qux; }; Where there would be a difference in size is struct foo { int bar; bool baz1:1; bool baz2:1; int qux; }; and struct foo { int bar; bool baz1; bool baz2; int qux; };