Re: [PATCH] checkpatch: Add a --strict test for structs with bool member definitions

[Julia Lawall]

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