linux-kernel - Re: [RFC] [PATCH] Fix b43 driver build for arm

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Date:	Sat, 23 Feb 2008 06:51:09 +0100
From:	Michael Buesch <mb@...sch.de>
To:	"Gordon Farquharson" <gordonfarquharson@...il.com>
Cc:	"Sam Ravnborg" <sam@...nborg.org>,
	"Russell King" <rmk+lkml@....linux.org.uk>,
	linux-kernel@...r.kernel.org, linville@...driver.com,
	stefano.brivio@...imi.it, "Linus Torvalds" <torvalds@...l.org>,
	"Andrew Morton" <akpm@...l.org>, viro@....linux.org.uk
Subject: Re: [RFC] [PATCH] Fix b43 driver build for arm

On Saturday 23 February 2008, Gordon Farquharson wrote:
> On Fri, Feb 22, 2008 at 7:07 AM, Michael Buesch <mb@...sch.de> wrote:
> > On Friday 22 February 2008 05:24:32 Gordon Farquharson wrote:
> >  > On Wed, Feb 20, 2008 at 12:37 PM, Sam Ravnborg <sam@...nborg.org> wrote:
> >  >
> >  > >  Option 1) is the worst of the three as that can cost
> >  > >  of many hours bug-hunting.
> >  > >  Option 3) may seem optimal but I do not like to add more
> >  > >  complexity to this part of the build. And really I do not
> >  > >  know a reliable way to detech when we do cross builds anyway.
> >  > >
> >  > >  Leaving us with option 2) that is simple, strighforward and harmless.
> >  >
> >  > Are you willing to sign off on and commit the patch?
> >
> >  Only with a big fat comment added that the alignment is only needed
> >  because of a broken sanity check in file2alias.c.
> 
> How about this?
> 
> ---
> 
> Align the members of the SSB device structure to a 32 bit boundary so
> that the b43 driver can be built for arm using a cross compiler. This
> change is required so that the test in scripts/mod/file2alias.c that
> checks that the size of the device ID type against the size of the
> section in the object file succeeds (see
> http://lkml.org/lkml/2008/2/18/481 for discussion).
> 
> Signed-off-by: Gordon Farquharson <gordonfarquharson@...il.com>
> 
> ---
> 
> diff --git a/include/linux/mod_devicetable.h b/include/linux/mod_devicetable.h
> index 139d49d..93083ad 100644
> --- a/include/linux/mod_devicetable.h
> +++ b/include/linux/mod_devicetable.h
> @@ -351,7 +351,9 @@ struct sdio_device_id {
>  struct ssb_device_id {
>         __u16   vendor;
>         __u16   coreid;
> -       __u8    revision;
> +       /* Explicit padding to support cross-compilation. */

A big fat comment is something like that:

/* Explicit padding to support a broken sanity check in file2alias.c.
 * The check will compare the size of the structure in the kernel
 * object file to the userspace the kernel is compiled on.
 * This breaks on cross-compilation. This padding is a workaround
 * for this. */

> +       __u8    revision
> +               __attribute__((aligned(sizeof(__u32))));
>  };
>  #define SSB_DEVICE(_vendor, _coreid, _revision)  \
>         { .vendor = _vendor, .coreid = _coreid, .revision = _revision, }
> 


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