linux-kernel - Re: [PATCH v3 2/6] compiler.h: Introduce TYPEOF

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Message-ID: <CAFULd4Y7-_Zax3S-m3H6ok9SvsBgS7DmJjSu=3VZ1hyzT71jjg@mail.gmail.com>
Date: Tue, 10 Dec 2024 17:37:10 +0100
From: Uros Bizjak <ubizjak@...il.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: x86@...nel.org, linux-mm@...ck.org, linux-kernel@...r.kernel.org, 
	linux-bcachefs@...r.kernel.org, linux-arch@...r.kernel.org, 
	netdev@...r.kernel.org, Nadav Amit <nadav.amit@...il.com>, 
	Thomas Gleixner <tglx@...utronix.de>, Dennis Zhou <dennis@...nel.org>, Tejun Heo <tj@...nel.org>, 
	Christoph Lameter <cl@...ux.com>, Linus Torvalds <torvalds@...ux-foundation.org>, 
	Andy Lutomirski <luto@...nel.org>, Ingo Molnar <mingo@...nel.org>, Brian Gerst <brgerst@...il.com>, 
	Denys Vlasenko <dvlasenk@...hat.com>, "H. Peter Anvin" <hpa@...or.com>, 
	Nathan Chancellor <nathan@...nel.org>
Subject: Re: [PATCH v3 2/6] compiler.h: Introduce TYPEOF_UNQUAL() macro

On Mon, Dec 9, 2024 at 12:30 PM Peter Zijlstra <peterz@...radead.org> wrote:
>
> On Sun, Dec 08, 2024 at 09:45:17PM +0100, Uros Bizjak wrote:
> > Define TYPEOF_UNQUAL() to use __typeof_unqual__() as typeof operator
> > when available, to return unqualified type of the expression.
> >
> > Current version of sparse doesn't know anything about __typeof_unqual__()
> > operator. Avoid the usage of __typeof_unqual__() when sparse checking
> > is active to prevent sparse errors with unknowing keyword.
>
> Ooooh, new toys.
>
> I suppose __unqual_scalar_typeof() wants to be using this when
> available?

Not only that, the new toy enables clang to check kernel's address
spaces in a generic way using address_space attribute.

Please find attached a follow-up patch that enables __percpu checks
for all targets, supported by clang. Clang is a little bit pickier
than gcc about named address space declarations (it warns for use of
duplicated address space attribute), so the patch in addition to the
obvious

+#  define __percpu_qual        __attribute__((address_space(3)))

also fixes a couple of macros that could result in a duplicated
address space attribute.

The patch, applied as a follow-up to the series, survives allyesconfig
compilation with clang-19 and produces a bootable kernel. The patch
was tested only for x86_64 target, for other targets a couple of
trivial fixes would be necessary (a cast or a substitution of typeof()
with TYPEOF_UNQUAL()).

AFAICS, the same approach using clang's address_space attribute can be
implemented to also check other address spaces: __user, __iommu  and
__rcu.

Uros.

View attachment "percpu-clang.diff.txt" of type "text/plain" (2238 bytes)