linux-kernel - [PATCH v2 0/4] s390: Fix and optimize _

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Message-ID: <20250916134803.874580-1-hca@linux.ibm.com>
Date: Tue, 16 Sep 2025 15:47:59 +0200
From: Heiko Carstens <hca@...ux.ibm.com>
To: Nathan Chancellor <nathan@...nel.org>, Miguel Ojeda <ojeda@...nel.org>,
        Kees Cook <kees@...nel.org>,
        Nick Desaulniers <nick.desaulniers+lkml@...il.com>,
        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 v2 0/4] s390: Fix and optimize __flogr() inline assembly

v2:

- Split patches differently, so that the first patch is the actual
  fix, which addresses the reported warning / error. The subsequent
  patches are optimizations

v1:

https://lore.kernel.org/all/20250910151216.646600-1-hca@linux.ibm.com/

A recent optimization of the s390 specific ffs() and ffs64()
implementations leads to a new compiler warning. Instead of reverting the
optimization address this with the rather new assume attribute, which
generates even better code, if supported by compilers.

Since the assume attribute may be useful for others as well, add the
__assume macro to compiler attributes, so it is kernel wide available,
instead of adding an s390 specific optimization.

Heiko Carstens (4):
  s390/bitops: Limit return value range of __flogr()
  compiler_types: Add __assume macro
  s390/bitops: Use __assume() for __flogr() inline assembly return value
  s390/bitops: Cleanup __flogr()

 arch/s390/include/asm/bitops.h | 21 ++++++++++++++-------
 include/linux/compiler_types.h | 23 +++++++++++++++++++++++
 init/Kconfig                   | 10 ++++++++++
 3 files changed, 47 insertions(+), 7 deletions(-)

-- 
2.48.1