linux-kernel - Re: [PATCH v4 1/9] KVM: s390: Extend MEM_OP ioctl by storage key checked cmpxchg

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Date:   Wed, 4 Jan 2023 18:27:33 +0100
From:   Heiko Carstens <hca@...ux.ibm.com>
To:     Janis Schoetterl-Glausch <scgl@...ux.ibm.com>
Cc:     kernel test robot <lkp@...el.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Janosch Frank <frankja@...ux.ibm.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        oe-kbuild-all@...ts.linux.dev,
        David Hildenbrand <david@...hat.com>,
        Jonathan Corbet <corbet@....net>, kvm@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-kselftest@...r.kernel.org, linux-s390@...r.kernel.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Shuah Khan <skhan@...uxfoundation.org>,
        Sven Schnelle <svens@...ux.ibm.com>
Subject: Re: [PATCH v4 1/9] KVM: s390: Extend MEM_OP ioctl by storage key
 checked cmpxchg

On Mon, Dec 19, 2022 at 10:24:33PM +0100, Janis Schoetterl-Glausch wrote:
> On Wed, 2022-12-14 at 10:23 +0800, kernel test robot wrote:
> > Hi Janis,
> > 
> > Thank you for the patch! Yet something to improve:
> > All errors (new ones prefixed by >>):
> > 
> >    s390-linux-ld: arch/s390/kvm/gaccess.o: in function `__cmpxchg_user_key':
> > > > arch/s390/include/asm/uaccess.h:410: undefined reference to `__ashlti3'
> > > > s390-linux-ld: arch/s390/include/asm/uaccess.h:411: undefined reference to `__ashlti3'
> >    s390-linux-ld: arch/s390/include/asm/uaccess.h:458: undefined reference to `__ashlti3'
> >    s390-linux-ld: arch/s390/include/asm/uaccess.h:459: undefined reference to `__ashlti3'
> > 51098f0eb22e2f Janis Schoetterl-Glausch 2022-11-16 @410  		_old = (old & 0xff) << shift;
> > 51098f0eb22e2f Janis Schoetterl-Glausch 2022-11-16 @411  		_new = (new & 0xff) << shift;
> 
> Not sure what it is in this config that causes gcc to emit this
> symbol instead of a shift instruction, but casting old/new to 32 bit
> fixes the error.

Right.. now we have the same fun with 128 bit arithmetics that we had
with 64 bit arithmetics on 32 bit. I really missed that :)

Fixed the way you proposed it:
https://git.kernel.org/pub/scm/linux/kernel/git/s390/linux.git/commit/?h=cmpxchg_user_key&id=b33d59fb37ddcb6ee65d4fa23cc3d58793d13c5b