linux-kernel - Re: [PATCH 5.4-rc1 BUILD FIX] s390: mark __cpacf_query() as __always

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Date:   Wed, 2 Oct 2019 09:03:33 +0200
From:   Michal Kubecek <mkubecek@...e.cz>
To:     linux-kernel@...r.kernel.org
Cc:     Heiko Carstens <heiko.carstens@...ibm.com>,
        Jiri Kosina <jikos@...nel.org>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-s390@...r.kernel.org
Subject: Re: [PATCH 5.4-rc1 BUILD FIX] s390: mark __cpacf_query() as
 __always_inline

On Wed, Oct 02, 2019 at 08:46:05AM +0200, Heiko Carstens wrote:
> On Tue, Oct 01, 2019 at 10:08:01PM +0200, Jiri Kosina wrote:
> > 
> >    In file included from arch/s390/kvm/kvm-s390.c:44:
> >    ./arch/s390/include/asm/cpacf.h: In function '__cpacf_query':
> >    ./arch/s390/include/asm/cpacf.h:179:2: warning: asm operand 3 probably doesn't match constraints
> >      179 |  asm volatile(
> >          |  ^~~
> >    ./arch/s390/include/asm/cpacf.h:179:2: error: impossible constraint in 'asm'
> > 
> > ...
> > 
> > I am wondering how is it possible that none of the build-testing 
> > infrastructure we have running against linux-next caught this? Not enough 
> > non-x86 coverage?
> 
> Well, there is plenty of s390 coverage with respect to daily builds
> (also here). It doesn't fail for me with gcc 9.1; so you may either
> have a different gcc version or different config options(?) so the
> compiler decided to not inline the function.

I think I found the reason: we only hit the build failure with one
special config used for zfcpdump which has

  CONFIG_CC_OPTIMIZE_FOR_SIZE=y

When I switched to CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE=y (which we have
in other s390x configs and which most people probably prefer), the build
does not fail even without the patch.

Michal Kubecek