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Date: Tue, 30 Jan 2024 22:53:22 -0800
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Message-ID: <20240131065322.1126831-1-maskray@google.com>
Subject: [PATCH] arm64: jump_label: use constraint "S" instead of "i"
From: Fangrui Song <maskray@google.com>
To: Catalin Marinas <catalin.marinas@arm.com>, Will Deacon <will@kernel.org>, 
	linux-arm-kernel@lists.infradead.org
Cc: Jisheng Zhang <jszhang@kernel.org>, Ard Biesheuvel <ardb@kernel.org>, llvm@lists.linux.dev, 
	linux-kernel@vger.kernel.org, Fangrui Song <maskray@google.com>
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The constraint "i" seems to be copied from x86 (and with a redundant
modifier "c"). It works with -fno-PIE but not with -fPIE/-fPIC in GCC's
aarch64 port.

The constraint "S", which denotes a symbol reference (e.g. function,
global variable) or label reference, is more appropriate, and has been
available in GCC since 2012 and in Clang since 7.0.

Signed-off-by: Fangrui Song <maskray@google.com>
Link: https://maskray.me/blog/2024-01-30-raw-symbol-names-in-inline-assembly
---
 arch/arm64/include/asm/jump_label.h | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/include/asm/jump_label.h b/arch/arm64/include/asm/jump_label.h
index 48ddc0f45d22..31862b3bb33d 100644
--- a/arch/arm64/include/asm/jump_label.h
+++ b/arch/arm64/include/asm/jump_label.h
@@ -23,9 +23,9 @@ static __always_inline bool arch_static_branch(struct static_key * const key,
 		 "	.pushsection	__jump_table, \"aw\"	\n\t"
 		 "	.align		3			\n\t"
 		 "	.long		1b - ., %l[l_yes] - .	\n\t"
-		 "	.quad		%c0 - .			\n\t"
+		 "	.quad		%0 - .			\n\t"
 		 "	.popsection				\n\t"
-		 :  :  "i"(&((char *)key)[branch]) :  : l_yes);
+		 :  :  "S"(&((char *)key)[branch]) :  : l_yes);
 
 	return false;
 l_yes:
@@ -40,9 +40,9 @@ static __always_inline bool arch_static_branch_jump(struct static_key * const ke
 		 "	.pushsection	__jump_table, \"aw\"	\n\t"
 		 "	.align		3			\n\t"
 		 "	.long		1b - ., %l[l_yes] - .	\n\t"
-		 "	.quad		%c0 - .			\n\t"
+		 "	.quad		%0 - .			\n\t"
 		 "	.popsection				\n\t"
-		 :  :  "i"(&((char *)key)[branch]) :  : l_yes);
+		 :  :  "S"(&((char *)key)[branch]) :  : l_yes);
 
 	return false;
 l_yes:
-- 
2.43.0.429.g432eaa2c6b-goog