linux-kernel - [tip: x86/asm] x86/asm: Use %a instead of %P operand modifier in asm templates

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Date: Tue, 19 Mar 2024 12:31:39 -0000
From: "tip-bot2 for Uros Bizjak" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Uros Bizjak <ubizjak@...il.com>, Ingo Molnar <mingo@...nel.org>,
 Linus Torvalds <torvalds@...ux-foundation.org>,
 Josh Poimboeuf <jpoimboe@...hat.com>, Ard Biesheuvel <ardb@...nel.org>,
 "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
 linux-kernel@...r.kernel.org
Subject: [tip: x86/asm] x86/asm: Use %a instead of %P operand modifier in asm
 templates

The following commit has been merged into the x86/asm branch of tip:

Commit-ID:     d689863c1a60b9936b47a34fa5c3330de374f4fc
Gitweb:        https://git.kernel.org/tip/d689863c1a60b9936b47a34fa5c3330de374f4fc
Author:        Uros Bizjak <ubizjak@...il.com>
AuthorDate:    Tue, 19 Mar 2024 11:40:14 +01:00
Committer:     Ingo Molnar <mingo@...nel.org>
CommitterDate: Tue, 19 Mar 2024 13:15:35 +01:00

x86/asm: Use %a instead of %P operand modifier in asm templates

The "P" asm operand modifier is a x86 target-specific modifier.

For x86_64, when used with a symbol reference, the "%P" modifier
emits "sym" instead of "sym(%rip)". This property is currently
used to issue bare symbol reference.

The generic "a" operand modifier should be used instead. The "a"
asm operand modifier substitutes a memory 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.

Also note that unlike GCC, clang emits %rip-relative symbol
reference with "P" asm operand modifier, so the patch also unifies
symbol handling with both compilers.

No functional changes intended.

Signed-off-by: Uros Bizjak <ubizjak@...il.com>
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Josh Poimboeuf <jpoimboe@...hat.com>
Cc: Ard Biesheuvel <ardb@...nel.org>
Cc: "H. Peter Anvin" <hpa@...or.com>
Link: https://lore.kernel.org/r/20240319104418.284519-4-ubizjak@gmail.com
---
 arch/x86/include/asm/cpufeature.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/cpufeature.h b/arch/x86/include/asm/cpufeature.h
index fa938ed..daae5c6 100644
--- a/arch/x86/include/asm/cpufeature.h
+++ b/arch/x86/include/asm/cpufeature.h
@@ -172,7 +172,7 @@ static __always_inline bool _static_cpu_has(u16 bit)
 		ALTERNATIVE_TERNARY("jmp 6f", %c[feature], "", "jmp %l[t_no]")
 		".pushsection .altinstr_aux,\"ax\"\n"
 		"6:\n"
-		" testb %[bitnum]," _ASM_RIP(%P[cap_byte]) "\n"
+		" testb %[bitnum], %a[cap_byte]\n"
 		" jnz %l[t_yes]\n"
 		" jmp %l[t_no]\n"
 		".popsection\n"