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Message-ID: <alpine.DEB.2.20.1804142315300.2750@hadrien> Date: Sat, 14 Apr 2018 23:19:09 +0200 (CEST) From: Julia Lawall <julia.lawall@...6.fr> To: Joe Perches <joe@...ches.com> cc: Julia Lawall <julia.lawall@...6.fr>, Andrew Morton <akpm@...ux-foundation.org>, Peter Zijlstra <peterz@...radead.org>, "Rafael J. Wysocki" <rafael@...nel.org>, Andy Whitcroft <apw@...onical.com>, yuankuiz@...eaurora.org, Linux PM <linux-pm@...r.kernel.org>, "Rafael J. Wysocki" <rjw@...ysocki.net>, Frederic Weisbecker <fweisbec@...il.com>, Thomas Gleixner <tglx@...utronix.de>, paulmck@...ux.vnet.ibm.com, Ingo Molnar <mingo@...nel.org>, Len Brown <len.brown@...el.com>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org> Subject: Re: [PATCH] checkpatch: Add a --strict test for structs with bool member definitions 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. julia
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