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Message-ID: <20231016200755.287403-1-ubizjak@gmail.com>
Date: Mon, 16 Oct 2023 22:07:30 +0200
From: Uros Bizjak <ubizjak@...il.com>
To: x86@...nel.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>
Subject: [PATCH] x86/percpu: Use correct asm operand modifier in percpu_stable_op
"P" asm operand modifier is a x86 target-specific modifier. When used
for a constant, it drops all syntax-specific prefixes and issues the
bare constant. This modifier is not correct for address handling,
in this case a generic "a" operand modifier should be used.
"a" asm operand modifier substitutes a nemory reference, with the
actual operand treated as address. For x86_64, when a symbol is
provided, the "a" modifier emits "sym(%rip)" instead of "sym",
enabling shorter %rip-relative addressing.
Clang allows only "i" and "r" opreand constraints with "a" modifier,
so the patch normalizes the modifier/constraint pair to "a"/"i"
which is consistent between both compilers.
The patch reduces code size of a test build for 4072 bytes:
25519196 4388300 808452 30715948 1d4b02c vmlinux-new.o
25523268 4388300 808452 30720020 1d4c014 vmlinux-old.o
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>
Signed-off-by: Uros Bizjak <ubizjak@...il.com>
---
arch/x86/include/asm/percpu.h | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/arch/x86/include/asm/percpu.h b/arch/x86/include/asm/percpu.h
index 54746903b8c3..ac3220aeb779 100644
--- a/arch/x86/include/asm/percpu.h
+++ b/arch/x86/include/asm/percpu.h
@@ -194,9 +194,9 @@ do { \
#define percpu_stable_op(size, op, _var) \
({ \
__pcpu_type_##size pfo_val__; \
- asm(__pcpu_op2_##size(op, __force_percpu_arg(P[var]), "%[val]") \
+ asm(__pcpu_op2_##size(op, __force_percpu_arg(a[var]), "%[val]") \
: [val] __pcpu_reg_##size("=", pfo_val__) \
- : [var] "p" (&(_var))); \
+ : [var] "i" (&(_var))); \
(typeof(_var))(unsigned long) pfo_val__; \
})
--
2.41.0
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