linux-kernel - [PATCH] x86/percpu: Declare const_pcpu

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Date:   Thu, 30 Nov 2023 17:27:35 +0100
From:   Uros Bizjak <ubizjak@...il.com>
To:     x86@...nel.org, linux-kernel@...r.kernel.org
Cc:     Uros Bizjak <ubizjak@...il.com>, kernel test robot <lkp@...el.com>,
        Andy Lutomirski <luto@...nel.org>,
        Brian Gerst <brgerst@...il.com>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        Ingo Molnar <mingo@...nel.org>,
        "H . Peter Anvin" <hpa@...or.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Josh Poimboeuf <jpoimboe@...hat.com>
Subject: [PATCH] x86/percpu: Declare const_pcpu_hot as extern const variable

const_pcpu_hot is aliased by linker to pcpu_hot, so there is no need
to use DECLARE_PER_CPU_ALIGNED macro. Also, declare const_pcpu_hot
as extern to avoid allocating storage space for the aliased structure.

Reported-by: kernel test robot <lkp@...el.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202311302257.tSFtZnly-lkp@intel.com/

Fixes: ed2f752e0e0a ("x86/percpu: Introduce const-qualified const_pcpu_hot to micro-optimize code generation")
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Brian Gerst <brgerst@...il.com>
Cc: Denys Vlasenko <dvlasenk@...hat.com>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Josh Poimboeuf <jpoimboe@...hat.com>
Signed-off-by: Uros Bizjak <ubizjak@...il.com>
---
 arch/x86/include/asm/current.h | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/current.h b/arch/x86/include/asm/current.h
index 0538d2436673..9fbd7cb2dc86 100644
--- a/arch/x86/include/asm/current.h
+++ b/arch/x86/include/asm/current.h
@@ -37,8 +37,7 @@ static_assert(sizeof(struct pcpu_hot) == 64);
 DECLARE_PER_CPU_ALIGNED(struct pcpu_hot, pcpu_hot);
 
 /* const-qualified alias to pcpu_hot, aliased by linker. */
-DECLARE_PER_CPU_ALIGNED(const struct pcpu_hot __percpu_seg_override,
-			const_pcpu_hot);
+extern const struct pcpu_hot __percpu_seg_override const_pcpu_hot;
 
 static __always_inline struct task_struct *get_current(void)
 {
-- 
2.42.0