[PATCH v2 4/4] x86/percpu: Introduce %rip-relative addressing to PER_CPU_VAR macro

Uros Bizjak
2023-10-12T20:18:07Z

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@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Uros Bizjak <ubizjak@gmail.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