linux-kernel - warning: cast removes address space '_

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Date: Sat, 30 Mar 2024 00:56:54 +0100
From: Charlemagne Lasse <charlemagnelasse@...il.com>
To: x86@...nel.org, LKML <linux-kernel@...r.kernel.org>, 
	Luc Van Oostenryck <lucvoo@...nel.org>
Cc: Uros Bizjak <ubizjak@...il.com>, Andy Lutomirski <luto@...nel.org>, Ingo Molnar <mingo@...nel.org>, 
	Nadav Amit <namit@...are.com>, Brian Gerst <brgerst@...il.com>, 
	Denys Vlasenko <dvlasenk@...hat.com>, "H . Peter Anvin" <hpa@...or.com>, 
	Linus Torvalds <torvalds@...ux-foundation.org>, Peter Zijlstra <peterz@...radead.org>, 
	Thomas Gleixner <tglx@...utronix.de>, Borislav Petkov <bp@...en8.de>, Josh Poimboeuf <jpoimboe@...hat.com>
Subject: warning: cast removes address space '__percpu' of expression

After switching to linux 6.9-rc1, I get a lot of these errors (when
compiling with cgcc/sparse):

/include/linux/netdevice.h:4033:17: warning: cast removes address
space '__percpu' of expression

This is around code which wasn't changed and which correctly uses the
per cpu helper. Sparse flags were -Wsparse-all for sparse 0.6.4
(latest release). Sparse was enabled via C=1 parameter and sparse was
configured using CHECK="sparse -Wsparse-all"

Problem was introduced between commit 8ae292c66dcb ("x86/lib: Address
kernel-doc warnings") and 3a1d3829e193 ("x86/percpu: Avoid sparse
warning with cast to named address space").

I would even go as far as saying that 1ca3683cc6d2 ("x86/percpu:
Enable named address spaces with known compiler version") together
with 3a1d3829e193 ("x86/percpu: Avoid sparse warning with cast to
named address space") triggered this problem