Re: [linux-next:master 12804/13809] include/linux/compiler.h:350:38: error: call to '__compiletime_assert_1533' declared with attribute error: BUILD_BUG_ON failed: __alignof__ *vq->avail > VRING_AVAIL_ALIGN_SIZE

["Michael S. Tsirkin" <mst@redhat.com>]

On Mon, Apr 06, 2020 at 12:00:36PM +0200, Ard Biesheuvel wrote:
> (adding some ARM GCC folks)
> 
> 
> On Sun, 5 Apr 2020 at 18:44, Michael S. Tsirkin <mst@redhat.com> wrote:
> >
> > Hello!
> > I would appreciate ARM maintainers take on the following
> > (sorry if I forgot someone, pls feel free to add people to CC):
> >
> >
> > On Sun, Apr 05, 2020 at 05:01:01AM -0400, Michael S. Tsirkin wrote:
> > > On Sun, Apr 05, 2020 at 07:57:24AM +0800, kbuild test robot wrote:
> > > > tree:   https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git master
> > > > head:   dff79597431045a775f2e5d4d9de31bfa0d32a34
> > > > commit: 20c384f1ea1a0bc7320bc445c72dd02d2970d594 [12804/13809] vhost: refine vhost and vringh kconfig
> > > > config: arm-randconfig-a001-20200405 (attached as .config)
> > > > compiler: arm-linux-gnueabi-gcc (GCC) 9.3.0
> > > > reproduce:
> > > >         wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
> > > >         chmod +x ~/bin/make.cross
> > > >         git checkout 20c384f1ea1a0bc7320bc445c72dd02d2970d594
> > > >         # save the attached .config to linux build tree
> > > >         GCC_VERSION=9.3.0 make.cross ARCH=arm
> > > >
> > > > If you fix the issue, kindly add following tag as appropriate
> > > > Reported-by: kbuild test robot <lkp@intel.com>
> > > >
> > > > All error/warnings (new ones prefixed by >>):
> > > >
> > > >    In file included from include/linux/kernel.h:11,
> > > >                     from include/linux/list.h:9,
> > > >                     from include/linux/preempt.h:11,
> > > >                     from include/linux/spinlock.h:51,
> > > >                     from include/linux/seqlock.h:36,
> > > >                     from include/linux/time.h:6,
> > > >                     from include/linux/stat.h:19,
> > > >                     from include/linux/fcntl.h:5,
> > > >                     from include/linux/eventfd.h:12,
> > > >                     from drivers/vhost/vhost.c:13:
> > > >    In function 'vhost_vring_set_addr',
> > > >        inlined from 'vhost_vring_set_num_addr' at drivers/vhost/vhost.c:1581:7,
> > > >        inlined from 'vhost_vring_ioctl' at drivers/vhost/vhost.c:1614:10:
> > > > >> include/linux/compiler.h:350:38: error: call to '__compiletime_assert_1533' declared with attribute error: BUILD_BUG_ON failed: __alignof__ *vq->avail > VRING_AVAIL_ALIGN_SIZE
> > > >      350 |  _compiletime_assert(condition, msg, __compiletime_assert_, __LINE__)
> > > >          |                                      ^
> > > >    include/linux/compiler.h:331:4: note: in definition of macro '__compiletime_assert'
> > > >      331 |    prefix ## suffix();    \
> > > >          |    ^~~~~~
> > > >    include/linux/compiler.h:350:2: note: in expansion of macro '_compiletime_assert'
> > > >      350 |  _compiletime_assert(condition, msg, __compiletime_assert_, __LINE__)
> > > >          |  ^~~~~~~~~~~~~~~~~~~
> > > >    include/linux/build_bug.h:39:37: note: in expansion of macro 'compiletime_assert'
> > > >       39 | #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
> > > >          |                                     ^~~~~~~~~~~~~~~~~~
> > > >    include/linux/build_bug.h:50:2: note: in expansion of macro 'BUILD_BUG_ON_MSG'
> > > >       50 |  BUILD_BUG_ON_MSG(condition, "BUILD_BUG_ON failed: " #condition)
> > > >          |  ^~~~~~~~~~~~~~~~
> > > > >> drivers/vhost/vhost.c:1533:2: note: in expansion of macro 'BUILD_BUG_ON'
> > > >     1533 |  BUILD_BUG_ON(__alignof__ *vq->avail > VRING_AVAIL_ALIGN_SIZE);
> > > >          |  ^~~~~~~~~~~~
> > >
> > > This compiler seems to be broken. We have:
> > > #define VRING_AVAIL_ALIGN_SIZE 2
> > > and
> > >
> > >         struct vring_avail __user *avail;
> > >
> > > and
> > > struct vring_avail {
> > >         __virtio16 flags;
> > >         __virtio16 idx;
> > >         __virtio16 ring[];
> > > };
> > >
> > > A compiler that decides to require alignment of > 2 bytes on
> > > a struct of packed u16's is likely broken in a bunch of other
> > > ways that just happen not to trigger a BUILD_BUG.
> > >
> > >
> > > The commit referenced just enables build on more platforms ...
> >
> > OK after some research, it seems that the issue triggers with
> > latest gcc too.
> > To trigger it, supply -mabi=apcs-gnu on command line.
> >
> > Dropping  -mabi=apcs-gnu fixes the build.
> >
> > I am still researching this flag.
> >
> 
> Is there a difference between __alignof__ *vq->avail and
> __alignof__(struct vring_avail) ?

Yes, the same.
I found this:
https://stackoverflow.com/questions/43786747/struct-layout-in-apcs-gnu-abi

Not sure how to interpret it ...
-- 
MST


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