Hi Greg,
On Sat, Jun 16, 2012 at 1:12 AM, Greg Kroah-Hartman
<gregkh@xxxxxxxxxxxxxxxxxxx> wrote:
On Fri, Jun 15, 2012 at 11:02:55PM +0200, Geert Uytterhoeven wrote:
On Fri, Jun 15, 2012 at 10:10 PM, Greg Kroah-Hartman
<gregkh@xxxxxxxxxxxxxxxxxxx> 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?
Yes, it's fixes it, so
Acked-by: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>
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 */
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
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