linux-kernel - Re: [cocci] [PATCH -mm] -funsigned-char, x86: make struct p4_event

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Date:   Thu, 3 Nov 2022 15:07:37 +0100
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     Julia Lawall <julia.lawall@...ia.fr>
Cc:     Kees Cook <keescook@...omium.org>, cocci@...ia.fr,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Alexey Dobriyan <adobriyan@...il.com>,
        akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
        mm-commits@...r.kernel.org, masahiroy@...nel.org,
        gregkh@...uxfoundation.org, andriy.shevchenko@...ux.intel.com,
        Stephen Rothwell <sfr@...b.auug.org.au>
Subject: Re: [cocci] [PATCH -mm] -funsigned-char, x86: make struct
 p4_event_bind::cntr signed array

On Thu, Nov 03, 2022 at 01:57:26PM +0100, Julia Lawall wrote:
> 
> 
> On Thu, 3 Nov 2022, Jason A. Donenfeld wrote:
> 
> > Hi Julia,
> >
> > On Thu, Nov 3, 2022 at 1:45 PM Julia Lawall <julia.lawall@...ia.fr> wrote:
> > > It should work now.
> >
> > Thanks!
> >
> > > However, without disable optional_qualifier, char is
> > > still matching signed char.  If you think that should be changed, I can do
> > > that.
> >
> > Does `optional_qualifier` disable other things that might be
> > interesting to have? If so, maybe this is less than ideal? If not,
> > maybe it doesn't matter?
> 
> Optional qualifier only allows a metavariable declared to have a certain
> type to match an expression that has the same type with signed, const, or
> verbatim in front of it.  Disabling it forces you to write our signed,
> const etc explicitly when you want them.  So rules may becomes more
> verbose.

Oh, huh. Maybe best to treat it as a different type then so that's not
required? I was also thinking that it doesn't totally make sense the way
it is now, in that `char` is *NOT* signed on many platforms, such as
arm. In 6.2, it'll be unsigned everywhere, for kernel code. So in the
general case, for coccinelle, it's a bit of a heisentype and so maybe
should be treated as distinct from `signed char` or `unsigned char`.

Jason