linux-kernel - [PATCH 1/2] x86/percpu: Fix "multiple identical address spaces specified for type" clang warning

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Date: Sun, 26 May 2024 19:55:52 +0200
From: Uros Bizjak <ubizjak@...il.com>
To: x86@...nel.org,
	llvm@...ts.linux.dev,
	linux-kernel@...r.kernel.org
Cc: Uros Bizjak <ubizjak@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...nel.org>,
	Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Nathan Chancellor <nathan@...nel.org>,
	Nick Desaulniers <ndesaulniers@...gle.com>,
	Bill Wendling <morbo@...gle.com>,
	Justin Stitt <justinstitt@...gle.com>
Subject: [PATCH 1/2] x86/percpu: Fix "multiple identical address spaces specified for type" clang warning

The clang build with named address spaces enabled currently fails with:

error: multiple identical address spaces specified for type [-Werror,-Wduplicate-decl-specifier]

The warning is emitted when accessing const_pcpu_hot structure,
which is already declared in __seg_gs named address space.

Use specialized accessor for __raw_cpu_read_const() instead, avoiding
redeclaring __seg_gs named address space via __raw_cpu_read().

Signed-off-by: Uros Bizjak <ubizjak@...il.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: "H. Peter Anvin" <hpa@...or.com>
Cc: Nathan Chancellor <nathan@...nel.org>
Cc: Nick Desaulniers <ndesaulniers@...gle.com>
Cc: Bill Wendling <morbo@...gle.com>
Cc: Justin Stitt <justinstitt@...gle.com>
---
 arch/x86/include/asm/percpu.h | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/percpu.h b/arch/x86/include/asm/percpu.h
index c55a79d5feae..aeea5c8a17de 100644
--- a/arch/x86/include/asm/percpu.h
+++ b/arch/x86/include/asm/percpu.h
@@ -160,7 +160,10 @@ do {									\
 	*(qual __my_cpu_type(pcp) *)__my_cpu_ptr(&(pcp)) = (val);	\
 } while (0)
 
-#define __raw_cpu_read_const(pcp)	__raw_cpu_read(, , pcp)
+#define __raw_cpu_read_const(pcp)					\
+({									\
+	*(typeof(pcp) *)(__force uintptr_t)(&(pcp));			\
+})
 
 #else /* !CONFIG_USE_X86_SEG_SUPPORT: */
 
-- 
2.42.0