[PATCH 1/2] x86/bitops: Use TZCNT mnemonic in

Uros Bizjak
2025-03-25T17:52:28Z

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>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
---
arch/x86/include/asm/bitops.h | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/bitops.h b/arch/x86/include/asm/bitops.h
index 100413aff640..bbaf75ea6703 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;
--
2.42.0