linux-kernel - [PATCH 3/3] s390/bitops: Remove volatile qualifier from flogr() inline assembly

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <20250910151216.646600-4-hca@linux.ibm.com>
Date: Wed, 10 Sep 2025 17:12:16 +0200
From: Heiko Carstens <hca@...ux.ibm.com>
To: Nathan Chancellor <nathan@...nel.org>, Miguel Ojeda <ojeda@...nel.org>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Juergen Christ <jchrist@...ux.ibm.com>
Cc: linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org,
        Sven Schnelle <svens@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>
Subject: [PATCH 3/3] s390/bitops: Remove volatile qualifier from flogr() inline assembly

The flogr() inline assembly has no side effects and generates the same
output if the input does not change. Therefore remove the volatile
qualifier to allow the compiler to optimize the inline assembly away,
if possible.

This also removes the superfluous '\n' which makes the inline assembly
appear larger than it is according to compiler heuristics (number of
lines).

Suggested-by: Juergen Christ <jchrist@...ux.ibm.com>
Signed-off-by: Heiko Carstens <hca@...ux.ibm.com>
---
 arch/s390/include/asm/bitops.h | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/arch/s390/include/asm/bitops.h b/arch/s390/include/asm/bitops.h
index 46b90b545986..5e04836c9c8d 100644
--- a/arch/s390/include/asm/bitops.h
+++ b/arch/s390/include/asm/bitops.h
@@ -167,9 +167,8 @@ static __always_inline __attribute_const__ unsigned long __flogr(unsigned long w
 		union register_pair rp __uninitialized;
 
 		rp.even = word;
-		asm volatile(
-			"       flogr   %[rp],%[rp]\n"
-			: [rp] "+d" (rp.pair) : : "cc");
+		asm("flogr	%[rp],%[rp]"
+		    : [rp] "+d" (rp.pair) : : "cc");
 		bit = rp.even;
 		__assume(bit <= 64);
 		return bit & 127;
-- 
2.48.1