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From: Uros Bizjak <ubizjak@gmail.com>
Date: Tue, 2 Apr 2024 13:43:00 +0200
Message-ID: <CAFULd4YG21NdF_qNVBGDtXO6xnaYFeRPvKicB=gpgUUqYE=4jw@mail.gmail.com>
Subject: Re: arch/x86/include/asm/processor.h:698:16: sparse: sparse:
 incorrect type in initializer (different address spaces)
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>, kernel test robot <lkp@intel.com>, 
	oe-kbuild-all@lists.linux.dev, linux-kernel@vger.kernel.org, 
	Arjan van de Ven <arjan@linux.intel.com>, x86@kernel.org, 
	Luc Van Oostenryck <luc.vanoostenryck@gmail.com>, 
	Sparse Mailing-list <linux-sparse@vger.kernel.org>, "Paul E. McKenney" <paulmck@kernel.org>
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On Mon, Mar 4, 2024 at 8:07=E2=80=AFAM Thomas Gleixner <tglx@linutronix.de>=
 wrote:
>
> On Mon, Mar 04 2024 at 06:42, Uros Bizjak wrote:
>
> > On Mon, Mar 4, 2024 at 12:49=E2=80=AFAM Thomas Gleixner <tglx@linutroni=
x.de> wrote:
> >>
> >> On Sun, Mar 03 2024 at 21:24, Uros Bizjak wrote:
> >> > On Sun, Mar 3, 2024 at 9:21=E2=80=AFPM Uros Bizjak <ubizjak@gmail.co=
m> wrote:
> >> >> On Sun, Mar 3, 2024 at 9:10=E2=80=AFPM Thomas Gleixner <tglx@linutr=
onix.de> wrote:
> >> >> > That's so sad because it would provide us compiler based __percpu
> >> >> > validation.
> >> >>
> >> >> Unfortunately, the c compiler can't strip qualifiers, so typeof() i=
s
> >> >> of limited use also when const and volatile qualifiers are used.
> >> >> Perhaps some extension could be introduced to c standard to provide=
 an
> >> >> unqualified type, e.g. typeof_unqual().
> >> >
> >> > Oh, there is one in C23 [1].
> >>
> >> Yes. I found it right after ranting.
> >>
> >> gcc >=3D 14 and clang >=3D 16 have support for it of course only when =
adding
> >> -std=3Dc2x to the command line.
> >>
> >> Sigh. The name space qualifiers are non standard and then the thing
> >> which makes them more useful is hidden behind a standard.
> >
> > With GCC, you can use __typeof_unqual__ (please note underscores)
> > without -std=3Dc2x [1]:
> >
> > "... Alternate spelling __typeof_unqual__ is available in all C modes
> > and provides non-atomic unqualified version of what __typeof__
> > operator returns..."
> >
> > Please also see the example in my last post. It can be compiled without=
 -std=3D...
>
> With gcc >=3D 14. Not so with clang...

Please note that clang-17.0.6 currently fails to compile kernel with
named address spaces [1]. So perhaps kernel can use __typeof_unqual__
(available without -std=3Dc2x) in the hope that clang implements
__typeof_unqual__ in one of its next releases, following the examples
of GCC [2] and MSVC[3].

[1] https://lore.kernel.org/lkml/20240320173758.GA3017166@dev-arch.thelio-3=
990X/
[2] https://gcc.gnu.org/onlinedocs/gcc/Typeof.html
[3] https://learn.microsoft.com/en-us/cpp/c-language/typeof-unqual-c?view=
=3Dmsvc-170

Uros.