linux-kernel - [PATCH v2 4/4] x86/percpu: Introduce %rip-relative addressing to PER_CPU

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Message-ID: <20231012201743.292149-5-ubizjak@gmail.com>
Date:   Thu, 12 Oct 2023 22:12:07 +0200
From:   Uros Bizjak <ubizjak@...il.com>
To:     x86@...nel.org, xen-devel@...ts.xenproject.org,
        linux-kernel@...r.kernel.org
Cc:     Uros Bizjak <ubizjak@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Peter Zijlstra <peterz@...radead.org>
Subject: [PATCH v2 4/4] x86/percpu: Introduce %rip-relative addressing to PER_CPU_VAR macro

Introduce x86_64 %rip-relative addressing to PER_CPU_VAR macro.
Instruction with %rip-relative address operand is one byte shorter than
its absolute address counterpart and is also compatible with position
independent executable (-fpie) build.

Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: "H. Peter Anvin" <hpa@...or.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Signed-off-by: Uros Bizjak <ubizjak@...il.com>
---
 arch/x86/include/asm/percpu.h | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/arch/x86/include/asm/percpu.h b/arch/x86/include/asm/percpu.h
index 83e6a4bcea38..c53c5a7f8e78 100644
--- a/arch/x86/include/asm/percpu.h
+++ b/arch/x86/include/asm/percpu.h
@@ -4,19 +4,21 @@
 
 #ifdef CONFIG_X86_64
 #define __percpu_seg		gs
+#define __percpu_rel		(%rip)
 #else
 #define __percpu_seg		fs
+#define __percpu_rel
 #endif
 
 #ifdef __ASSEMBLY__
 
 #ifdef CONFIG_SMP
 #define PER_CPU_ARG(arg)	%__percpu_seg:arg
-#define PER_CPU_VAR(var)	%__percpu_seg:var
+#define PER_CPU_VAR(var)	%__percpu_seg:(var)##__percpu_rel
 #else /* ! SMP */
 #define PER_CPU_ARG(arg)	arg
-#define PER_CPU_VAR(var)	var
-#endif	/* SMP */
+#define PER_CPU_VAR(var)	(var)##__percpu_rel
+#endif /* SMP */
 
 #ifdef CONFIG_X86_64_SMP
 #define INIT_PER_CPU_VAR(var)  init_per_cpu__##var
-- 
2.41.0