From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753451AbcGDJPR (ORCPT ); Mon, 4 Jul 2016 05:15:17 -0400 Received: from mout.kundenserver.de ([212.227.17.13]:64432 "EHLO mout.kundenserver.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753256AbcGDJPO (ORCPT ); Mon, 4 Jul 2016 05:15:14 -0400 From: Arnd Bergmann To: linux-arm-kernel@lists.infradead.org Cc: Geert Uytterhoeven , "linux-kernel@vger.kernel.org" , kvm@vger.kernel.org, virtualization@lists.linux-foundation.org Subject: Re: Build regressions/improvements in v4.7-rc6 Date: Mon, 04 Jul 2016 11:17:48 +0200 Message-ID: <6183003.0tbSMroAbk@wuerfel> User-Agent: KMail/5.1.3 (Linux/4.4.0-22-generic; KDE/5.18.0; x86_64; ; ) In-Reply-To: References: <1467619946-424-1-git-send-email-geert@linux-m68k.org> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="us-ascii" X-Provags-ID: V03:K0:XBkxIx6Opk5uBZrvLcTp0cEapWo+rPD4EWuQeJ+unqzdH/L5imS kqTMoF/IIS6W/tpgFZjPoLj8eXgl8aHlwVHZipL59x3rnbJkiNiZRUtLR49B0InO7lrxGMm Au63iMfdJeF5IRnBNYxZGx5saxfbZtkBZ+67ukqshJdi2a4kPA2IFoF+paBvLZhcP1sA+c1 RD7jhzQvf5HrhFBFWU8bQ== X-UI-Out-Filterresults: notjunk:1;V01:K0:/byNTNWle4c=:Flpxz/flCJHOpxl7BcL6cE BP+Mggk3FCL30YJ/TFFnk50fwvi+2+eGjITOr+O+bOn8u5wZMNt95Y7LmOugMH5pPqwUUX/Jo JjwMlh7e671cw7c9+jEKzyBIlff2xkg+QcQrvH6F4HfWZXj+IVxzdfM0K2B+u+swKj0K+BDga Xp92H8htmUlV4FoG3/S4nMqnsBg0Ya7FC4lYfcsLXC8rtOTTqfXkpt5l4m6RolMGRLjBV4nMv 9eX6BHX3qSBT9Tn5LktL1kK447T6HFxf84lqLQTZACaStKMIdsnmMkhq9+pCYEfi2vlqL/OQG Uifvv5ktrJdUXWjNpy1b+dog19w8ktY50E7ScubFcix/ha8fU6R8Pa+eHN9SqSoEaQ+7R910R /NP3HfAUIxDAYMrv8jpLxVrurY6YbUvEY9mv50krbmPqs0BRfi3NDLeA9W6ly1mFF9mzfE0FY fRr4ZQJ9R1WY3PUkdeec5W7qAZiLNTk5kxhYNSfumvdTNLG9nUZWyC9D0WlgvBoKldsTIeZLo svjrv6+Pkdb4G8P3YVOyDuy5NOxJ5bOHnb7s9gHTJVraGAVIQG8E7I9aSYWV6ts6XcCNB2XRq KMcnW4Grvkyxej2zDgHueuK8mmR/RJ61/d1pfb+Lz+y/Jiuv5jvdGgCOjWMQf+SMIC50+eDSH PrTMMLSYg07ami0PaO2d+n7zkhnt1Ap8qNJJMUo5dvxT6+fwa9Pu1nK4Tm2jfWT6EeySbbBbK iy04ealMf7JaVm7f Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Monday, July 4, 2016 10:21:45 AM CEST Geert Uytterhoeven wrote: > On Mon, Jul 4, 2016 at 10:12 AM, Geert Uytterhoeven > wrote: > > JFYI, when comparing v4.7-rc6[1] to v4.7-rc5[3], the summaries are: > > - build errors: +3/-2 > > + /home/kisskb/slave/src/drivers/vhost/vhost.c: error: call to > '__compiletime_assert_844' declared with attribute error: BUILD_BUG_ON > failed: __alignof__ *vq->avail > VRING_AVAIL_ALIGN_SIZE: => 844:3 > > arm-randconfig > > > [1] http://kisskb.ellerman.id.au/kisskb/head/10562/ (260 out of 263 configs) > > [3] http://kisskb.ellerman.id.au/kisskb/head/10532/ (260 out of 263 configs) I don't see any changes in the code in this time frame, but this is the code causing it: struct vring_avail { __virtio16 flags; __virtio16 idx; __virtio16 ring[]; }; /* The virtqueue structure describes a queue attached to a device. */ struct vhost_virtqueue { struct vhost_dev *dev; /* The actual ring of buffers. */ struct mutex mutex; unsigned int num; struct vring_desc __user *desc; struct vring_avail __user *avail; struct vring_used __user *used; ... }; struct vhost_virtqueue *vq; BUILD_BUG_ON(__alignof__ *vq->avail > VRING_AVAIL_ALIGN_SIZE); The alignment of the *vq->avail should be '2' on all architectures, however an ARM OABI compiler will have a padded structure with alignment '4'. Looking at the build logs, I find it only in a single randconfig build at http://kisskb.ellerman.id.au/kisskb/buildresult/12735927/ which apparently enabled the vhost driver in combination with ARM_AEABI=n. In my own randconfig builds I am forcing ARM_AEABI=y because there are a couple of other problems with OABI. If we want to avoid this one, we could make the inclusion of drivers/vhost/Kconfig from arch/arm/kvm/Kconfig depend on CONFIG_AEABI, or perhaps go further force-enable CONFIG_AEABI for ARMv6k and higher (cmpxchg64() is broken on OABI too), and only include vhost if KVM is enabled (KVM in turn requires ARMv7). Arnd