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    SubjectRe: [-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.
    On Fri, Jun 15, 2012 at 11:02:55PM +0200, Geert Uytterhoeven wrote:
    > Hi Greg,
    >
    > On Fri, Jun 15, 2012 at 10:10 PM, Greg Kroah-Hartman
    > <gregkh@linuxfoundation.org> wrote:
    > > On Fri, Jun 15, 2012 at 07:42:08PM +0200, Geert Uytterhoeven wrote:
    > >> commit 81df2d594340dcb6d1a02191976be88a1ca8120c ("USB: allow match
    > >> on bInterfaceNumber") added a byte to the interior of struct usb_device_id,
    > >> enabling implicit padding:
    > >>
    > >> --- a/include/linux/mod_devicetable.h
    > >> +++ b/include/linux/mod_devicetable.h
    > >> @@ -115,6 +118,9 @@ struct usb_device_id {
    > >>         __u8            bInterfaceSubClass;
    > >>         __u8            bInterfaceProtocol;
    > >>
    > >> +       /* Used for vendor-specific interface matches */
    > >> +       __u8            bInterfaceNumber;
    > >> +
    > >>         /* not matched against */
    > >>         kernel_ulong_t  driver_info;
    > >>  };
    > >>
    > >> On m68k, this causes failures like:
    > >>
    > >> | 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.
    > >> | Fix definition of struct usb_device_id in mod_devicetable.h
    > >>
    > >> M68k is special in that it uses 2 for the alignment of 32-bit entities, hence
    > >> sizeof(struct usb_device_id) = 22.
    > >>
    > >> However, when cross-compiling on amd64, sizeof(struct usb_device_id) = 24
    > >> in scripts/mod/file2alias.c.
    > >
    > > I don't really understand, what is the problem here?  The fact that we
    > > added one byte to the structure?  And now something breaks?  How?
    > >
    > > What can we do to resolve it?
    >
    > 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.

    > 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))));
    };

    /* Some useful macros to use to create struct usb_device_id */
    --
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