linux-kernel - Re: [kbuild-all] drivers/vhost/vhost.c:718:3: error: call to '__compiletime_assert_718' declared with attribute error: BUILD_BUG_ON failed: __alignof__ *vq->avail > VRING_AVAIL_ALIGN_SIZE

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Date:	Thu, 10 Mar 2016 08:49:24 +0800
From:	Fengguang Wu <fengguang.wu@...el.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	jonas@...thpole.se, Philip Li <philip.li@...el.com>,
	linux@...ts.openrisc.net, kbuild-all@...org,
	linux-kernel@...r.kernel.org, Tony Breeds <tony@...eyournoodle.com>
Subject: Re: [kbuild-all] drivers/vhost/vhost.c:718:3: error: call to
 '__compiletime_assert_718' declared with attribute error: BUILD_BUG_ON
 failed: __alignof__ *vq->avail > VRING_AVAIL_ALIGN_SIZE

Hi Michael,

On Sun, Mar 06, 2016 at 10:37:07AM +0200, Michael S. Tsirkin wrote:
> I keep seeing these errors. Any openrisc/gcc/kbuild people
> interested in looking into this?

Sorry, currently the buildbot is running old gcc 4.5.1 cross compiler
for openrisc:

https://www.kernel.org/pub/tools/crosstool/files/bin/x86_64/4.5.1/x86_64-gcc-4.5.1-nolibc_or32-linux.tar.xz

I'll blacklist this error for now, until we upgraded to a new gcc
version that has this issue fixed.

Thanks,
Fengguang

> On Sun, Feb 28, 2016 at 07:15:14AM +0800, kbuild test robot wrote:
> > Hi Michael,
> > 
> > FYI, the error/warning still remains.
> > 
> > tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> > head:   691429e13dfaf5b0994b07cc166db41bd608ee3d
> > commit: 5d9a07b0de512b77bf28d2401e5fe3351f00a240 vhost: relax used address alignment
> > date:   1 year, 2 months ago
> > config: openrisc-allmodconfig (attached as .config)
> > reproduce:
> >         wget https://git.kernel.org/cgit/linux/kernel/git/wfg/lkp-tests.git/plain/sbin/make.cross -O ~/bin/make.cross
> >         chmod +x ~/bin/make.cross
> >         git checkout 5d9a07b0de512b77bf28d2401e5fe3351f00a240
> >         # save the attached .config to linux build tree
> >         make.cross ARCH=openrisc 
> > 
> > All errors (new ones prefixed by >>):
> > 
> >    drivers/vhost/vhost.c: In function 'vhost_vring_ioctl':
> > >> drivers/vhost/vhost.c:718:3: error: call to '__compiletime_assert_718' declared with attribute error: BUILD_BUG_ON failed: __alignof__ *vq->avail > VRING_AVAIL_ALIGN_SIZE
> > 
> > vim +/__compiletime_assert_718 +718 drivers/vhost/vhost.c
> > 
> >    712			    (u64)(unsigned long)a.avail_user_addr != a.avail_user_addr) {
> >    713				r = -EFAULT;
> >    714				break;
> >    715			}
> >    716	
> >    717			/* Make sure it's safe to cast pointers to vring types. */
> >  > 718			BUILD_BUG_ON(__alignof__ *vq->avail > VRING_AVAIL_ALIGN_SIZE);
> >    719			BUILD_BUG_ON(__alignof__ *vq->used > VRING_USED_ALIGN_SIZE);
> >    720			if ((a.avail_user_addr & (VRING_AVAIL_ALIGN_SIZE - 1)) ||
> >    721			    (a.used_user_addr & (VRING_USED_ALIGN_SIZE - 1)) ||
> > 
> > ---
> > 0-DAY kernel test infrastructure                Open Source Technology Center
> > https://lists.01.org/pipermail/kbuild-all                   Intel Corporation
> 
> I still think it's a bug in the openrisc compiler used.
> 
> struct vring_avail {
>         unsigned short flags;
>         unsigned short idx;
> };
> 
> struct vring_avail *x;
> 
> int main(int argc, char **argv)
> {
> 
>         footest();
>         if (__alignof__(*x) == 1)
>                 foo1();
>         else if (__alignof__(*x) == 2)
>                 foo2();
>         else if (__alignof__(*x) == 4)
>                 foo4();
>         else if (__alignof__(*x) == 8)
>                 foo8();
>         else
>                 fooother();
>         return 0;
> }
> 
> when compiled with the openrisc compiler from kernel.org this calls foo4
> and it really should call foo2, since the openrisc manual says:
> 
> 16.1.2
> Aggregates and Unions
> Aggregates (structures and arrays) and unions assume the alignment of
> their most
> strictly aligned element.
> 
> and alignment for unsigned short is 2.
> 
> 
> 
> -- 
> MST
> _______________________________________________
> kbuild-all mailing list
> kbuild-all@...ts.01.org
> https://lists.01.org/mailman/listinfo/kbuild-all

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