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

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Date: Sat, 2 Mar 2024 14:49:15 -0800
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: Thomas Gleixner <tglx@...utronix.de>
Cc: kernel test robot <lkp@...el.com>, oe-kbuild-all@...ts.linux.dev, 
	linux-kernel@...r.kernel.org, Arjan van de Ven <arjan@...ux.intel.com>, x86@...nel.org, 
	Luc Van Oostenryck <luc.vanoostenryck@...il.com>, 
	Sparse Mailing-list <linux-sparse@...r.kernel.org>
Subject: Re: arch/x86/include/asm/processor.h:698:16: sparse: sparse:
 incorrect type in initializer (different address spaces)

On Sat, 2 Mar 2024 at 14:00, Thomas Gleixner <tglx@...utronix.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