Re: arch/x86/include/asm/processor.h:698:16: sparse: sparse: incorrect type in initializer (different address spaces)

From: Linus Torvalds <torvalds@linux-foundation.org>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: 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>
Subject: Re: arch/x86/include/asm/processor.h:698:16: sparse: sparse: incorrect type in initializer (different address spaces)
Date: Sat, 2 Mar 2024 14:49:15 -0800	[thread overview]
Message-ID: <CAHk-=wiWhfdc4Sw2VBq_2nL2NDxmZS32xG4P7mBVwABGqUoJnw@mail.gmail.com> (raw)
In-Reply-To: <87le70uwf0.ffs@tglx>

On Sat, 2 Mar 2024 at 14:00, Thomas Gleixner <tglx@linutronix.de> wrote:
>
> I had commented out both. But the real reason is the EXPORT_SYMBOL,
> which obviously wants to be EXPORT_PER_CPU_SYMBOL_GPL...

Side note: while it's nice to hear that sparse kind of got this right,
I wonder what gcc does when we start using the named address spaces
for percpu variables.

We actively make EXPORT_PER_CPU_SYMBOL_XYZ be a no-op for sparse
exactly because sparse ended up warning about the regular
EXPORT_SYMBOL, and we didn't have any "real" per-cpu export model.

So EXPORT_PER_CPU_SYMBOL_GPL() is kind of an artificial "shut up
sparse". But with __seg_gs/fs support for native percpu symbols with
gcc, I wonder if we'll hit the same thing. Or is there something that
makes gcc not warn about the named address spaces?

Because in many ways the gcc named address spaces _should_ be pretty
much equivalent to the sparse ones.

            Linus