From: Uros Bizjak <ubizjak@gmail.com>
Date: Tue, 25 Mar 2025 17:52:01 +0000 (+0100)
Subject: x86/bitops: Use TZCNT mnemonic in <asm/bitops.h>
X-Git-Tag: v6.16-rc1~195^2~32^2~17
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=0717b1392dc7e3f350e5a5d25ea794aa92210684;p=thirdparty%2Fkernel%2Flinux.git

x86/bitops: Use TZCNT mnemonic in <asm/bitops.h>

Current minimum required version of binutils is 2.25,
which supports TZCNT instruction mnemonic.

Replace "REP; BSF" in variable__{ffs,ffz}() function
with this proper mnemonic.

No functional change intended.

Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lore.kernel.org/r/20250325175215.330659-1-ubizjak@gmail.com
---

diff --git a/arch/x86/include/asm/bitops.h b/arch/x86/include/asm/bitops.h
index 100413aff6402..bbaf75ea6703b 100644
--- a/arch/x86/include/asm/bitops.h
+++ b/arch/x86/include/asm/bitops.h
@@ -248,7 +248,7 @@ arch_test_bit_acquire(unsigned long nr, const volatile unsigned long *addr)
 
 static __always_inline unsigned long variable__ffs(unsigned long word)
 {
-	asm("rep; bsf %1,%0"
+	asm("tzcnt %1,%0"
 		: "=r" (word)
 		: ASM_INPUT_RM (word));
 	return word;
@@ -267,7 +267,7 @@ static __always_inline unsigned long variable__ffs(unsigned long word)
 
 static __always_inline unsigned long variable_ffz(unsigned long word)
 {
-	asm("rep; bsf %1,%0"
+	asm("tzcnt %1,%0"
 		: "=r" (word)
 		: "r" (~word));
 	return word;