linux-kernel - Re: [PATCH] Fix/add raw1394 CONFIG

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Date:	Mon, 21 May 2007 09:28:01 +0200
From:	Stefan Richter <stefanr@...6.in-berlin.de>
To:	dan@...nedy.org
CC:	Arnd Bergmann <arnd@...db.de>,
	Petr Vandrovec <petr@...drovec.name>,
	linux1394-devel@...ts.sourceforge.net, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Fix/add raw1394 CONFIG_COMPAT code

I wrote:
> Arnd Bergmann wrote:
>>>> Note that this data structure only needs conversion on x86_64 and ia64, but
>>>> not on powerpc and other 64 bit architectures that align __u64 also in
>>>> 32 bit mode.
...
> maybe we should change
> 
> /* argument to RAW1394_IOC_GET_CYCLE_TIMER ioctl */
> struct raw1394_cycle_timer {
...
> 	__u32 cycle_timer;
...
> 	__u64 local_time;
> };
> 
> to
> 
> /* argument to RAW1394_IOC_GET_CYCLE_TIMER ioctl */
> struct raw1394_cycle_timer {
...
> 	__u64 cycle_timer;
...
> 	__u64 local_time;
> };
> 
> before a libraw1394 with get-cycle-timer support is released.

On the other hand, we could handle it in the compat code alone and leave
the rest as-is.

/* PPC32 aligns this at 64bit, IA32 packs it */
struct raw1394_cycle_timer32 {
	__u32 cycle_timer;
	__u64 local_time;
}
#if defined(CONFIG_X86_64) || defined(CONFIG_IA64)
__attribute__((packed))
#endif
;

Eventually, Arnd's suggestion

> I would suggest you introduce a new __compat_u64 type as
> 
> typedef __u64 __compat_u64 __attribute__((aligned(4)));
> 
> in include/asm-{x86_64,ia64}/compat.h and as
> 
> typdef __u64 __compat_u64;
> 
> in the other architectures. Other people have hit the same problem
> before and found varying workarounds, but I think we should just
> do it correctly now.

should be put into practice though.
-- 
Stefan Richter
-=====-=-=== -=-= =-=-=
http://arcgraph.de/sr/
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