Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757111Ab2FPNXm (ORCPT ); Sat, 16 Jun 2012 09:23:42 -0400 Received: from canardo.mork.no ([148.122.252.1]:35953 "EHLO canardo.mork.no" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756798Ab2FPNXk convert rfc822-to-8bit (ORCPT ); Sat, 16 Jun 2012 09:23:40 -0400 From: =?utf-8?Q?Bj=C3=B8rn_Mork?= To: Greg Kroah-Hartman Cc: Geert Uytterhoeven , USB list , linux-kernel@vger.kernel.org, Linux-Next , linux-kbuild , Linux/m68k Subject: Re: [-next] FATAL: drivers/gpu/drm/udl/udl: sizeof(struct usb_device_id)=24 is not a modulo of the size of section __mod_usb_device_table=44. Organization: m References: <20120615201021.GB14544@kroah.com> <20120615231220.GC8205@kroah.com> Date: Sat, 16 Jun 2012 15:23:31 +0200 In-Reply-To: <20120615231220.GC8205@kroah.com> (Greg Kroah-Hartman's message of "Fri, 15 Jun 2012 16:12:20 -0700") Message-ID: <87lijns84s.fsf@nemi.mork.no> User-Agent: Gnus/5.11002 (No Gnus v0.20) Emacs/23.4 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3724 Lines: 99 Greg Kroah-Hartman writes: > On Fri, Jun 15, 2012 at 11:02:55PM +0200, Geert Uytterhoeven wrote: > >> As "kernel_ulong_t  driver_info" is no longer naturally aligned, the >> compiler will >> add implicit padding. But the padding depends on the architecture. > > Ah, so we were "lucky" before, nice. I don't really believe in luck :-) I think someone has been really smart here. Maybe too smart... >> It can be fixed by adding explicit padding. Probably it should be padded by >> 7 bytes (not 3), as kernel_ulong_t may require 8-byte alignment on some 64-bit >> platforms. Or by an explicit alignment attribute. >> >> See also >> * commit 8175fe2dda1c93a9c596921c8ed4a0b4baccdefe ("HID: fix >> hid_device_id for cross compiling") >> * commit 7492d4a416d68ab4bd254b36ffcc4e0138daa8ff ("sdio: fix module >> device table definition for m68k") >> * commit 9e2d3cd34a159948dc753a14573e16bffc04dba8 ("[PATCH] >> mod_devicetable.h fixes") > > So would the patch below fix this? It should force alignment of the > driver_data field, which is all you want here, right? > >> Still, there's a bug in file2alias (which is compiled by the host >> compiler), in that >> it may use different padding than the target platform when cross-compiling. > > That's not good, but outside of this specific issue, right? Have we > just been fortunate it hasn't really hit us yet? > > thanks, > > greg k-h > > diff --git a/include/linux/mod_devicetable.h b/include/linux/mod_devicetable.h > index 7771d45..6955045 100644 > --- a/include/linux/mod_devicetable.h > +++ b/include/linux/mod_devicetable.h > @@ -122,7 +122,8 @@ struct usb_device_id { > __u8 bInterfaceNumber; > > /* not matched against */ > - kernel_ulong_t driver_info; > + kernel_ulong_t driver_info > + __attribute__((aligned(sizeof(kernel_ulong_t)))); > }; This feels a lot like papering over the real problem. It will solve this instance, but the list of such previous "paper work" that Geert provided should be enough evidence that this will happen again the next time someone modifies a device id struct for some subsystem. And adding forced aligment here feels wrong since there is no good reason why the (target) compiler shouldn't know the proper alignment for this structure, is there? OK, "feels wrong" is not a good argument. But it would be better to solve this problem once and for all. AFAIK (which admittedly is not much wrt cross building) there is no way we can make the host built file2alias know the proper aligment for the structure in the target built modules. That's the background for this fix: commit 4ce6efed48d736e3384c39ff87bda723e1f8e041 Author: Sam Ravnborg Date: Sun Mar 23 21:38:54 2008 +0100 kbuild: soften modpost checks when doing cross builds The module alias support in the kernel have a consistency check where it is checked that the size of a structure in the kernel and on the build host are the same. For cross builds this check does not make sense so detect when we do cross builds and silently skip the check in these situations. This fixes a build bug for a wireless driver when cross building for arm. What I'm now wondering is why didn't this kick in? I believe we should find and fix that instead of playing around with the in-kernel structure alignments. If that's possible. BTW, thanks for finding and reporting this at such an early stage, Geert. Bjørn -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/