Received-SPF: pass (google.com: domain of linux-kernel+bounces-89896-linux.lists.archive=gmail.com@vger.kernel.org designates 2604:1380:4601:e00::3 as permitted sender) client-ip=2604:1380:4601:e00::3;
Precedence: bulk
MIME-Version: 1.0
References: <202403020457.RCJoQ3ts-lkp@intel.com> <87edctwr6y.ffs@tglx>
 <87a5nhwpus.ffs@tglx> <87y1b0vp8m.ffs@tglx> <87sf18vdsq.ffs@tglx>
 <87le70uwf0.ffs@tglx> <CAHk-=wiWhfdc4Sw2VBq_2nL2NDxmZS32xG4P7mBVwABGqUoJnw@mail.gmail.com>
 <87edcruvja.ffs@tglx> <CAFULd4bVEUBEidTLbHNzRaJbSjXm99yC8LT=jdzFWb7xnuFH7g@mail.gmail.com>
 <87bk7vuldh.ffs@tglx>
In-Reply-To: <87bk7vuldh.ffs@tglx>
From: Uros Bizjak <ubizjak@gmail.com>
Date: Sun, 3 Mar 2024 21:21:21 +0100
Message-ID: <CAFULd4arHT+_fy9_oUNpmsvyfVPGaeB_pdeuqVS3UTpP5R757A@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>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable

On Sun, Mar 3, 2024 at 9:10=E2=80=AFPM Thomas Gleixner <tglx@linutronix.de>=
 wrote:
>
> On Sun, Mar 03 2024 at 20:03, Uros Bizjak wrote:
> > On Sun, Mar 3, 2024 at 5:31=E2=80=AFPM Thomas Gleixner <tglx@linutronix=
de> wrote:
> >> I did not follow the __set_gs work closely, so I don't know whether Ur=
os
> >> ever tried to actually mark the per CPU variable __set_gs right away,
> >> which would obviously catch the above 'foo' nonsense.
> >
> > No, because [1]:
> >
> > "gcc does not provide a way to remove segment qualifiers, which is need=
ed
> > to use typeof() to create local instances of the per-cpu variable. For
> > this reason, do not use the segment qualifier for per-cpu variables, an=
d
> > do casting using the segment qualifier instead."
>
> Right. I just figured that out myself when playing with it in user
> space.
>
> That's so sad because it would provide us compiler based __percpu
> validation.

Unfortunately, the c compiler can't strip qualifiers, so typeof() is
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().

Uros.

> Right now this simply does not work and __verify_pcp_ptr(ptr) is not
> doing anything except when sparse looks at it.
>
> Sigh.
>
>         tglx
>