linux-kernel - RE: scripts/mod/file2alias.c cross compile problem

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Date:	Fri, 03 Aug 2007 08:08:20 +1000
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	"Luck, Tony" <tony.luck@...el.com>
Cc:	trenn@...e.de, Adrian Bunk <bunk@...sta.de>,
	Sam Ravnborg <sam@...nborg.org>, Jan Dittmer <jdi@....org>,
	Len Brown <lenb@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-ia64@...r.kernel.org
Subject: RE: scripts/mod/file2alias.c cross compile problem

On Thu, 2007-08-02 at 09:25 -0700, Luck, Tony wrote:
> > Adrian Bunk: scripts/mod/file2alias.c is compiled with HOSTCC and ensures that
> > kernel_ulong_t is correct, but it can't cope with different padding on
> > different architectures.
> 
> Surely this is the root cause ... you can't expect that the alignment
> rules of HOSTCC to make any sense for an arbitraty target.
> 
> > +#define FILLUP_LEN	7 /* dirty fix for i386 -> 64bit cross-compilation */
> >  
> >  struct acpi_device_id {
> >  	__u8 id[ACPI_ID_LEN];
> > +	__u8 dummy[FILLUP_LEN];
> >  	kernel_ulong_t driver_data;
> >  };
> 
> What's so special about this structure that we get an error?

It's in mod_devicetable.h: see comment at top of that file.  These
structures serve dual purpose: to describe the capabilities of the
driver to the kernel probing functions, *and* to export them to
userspace tables.  The former purpose is why there's a data pointer in
there.

scripts/mod/file2alias is the program that reads this: although it can
be altered to parse 32-vs-64, Adrian's fix is the simplest.

Hope that clarifies,
Rusty.

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