linux-kernel - Re: [PATCH] m68k: Use generic strncpy_from_user(), strlen_user(), and strnlen

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Date:	Thu, 7 Jun 2012 21:10:19 +1000
From:	Greg Ungerer <gerg@...pgear.com>
To:	Geert Uytterhoeven <geert@...ux-m68k.org>
CC:	Philippe De Muyter <phdm@...qel.be>,
	Greg Ungerer <gerg@...inux.org>,
	<linux-m68k@...ts.linux-m68k.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] m68k: Use generic strncpy_from_user(), strlen_user(),
 and strnlen_user()

Hi Geert,

On 06/07/2012 03:46 AM, Geert Uytterhoeven wrote:
> On Wed, Jun 6, 2012 at 8:31 AM, Greg Ungerer<gerg@...pgear.com>  wrote:
>> Yes, looks like that should have a "|| defined(CONFIG_CPU32)".
>> (According to the CPU32 reference manual words and long words must
>> be aligned on word boundaries.)
>>
>> I think something like CONFIG_CPU_HAS_NO_UNALIGNED makes sense.
>
> OK, doing that now...
>
> Then I saw arch/m68k/lib/memcpy.c.
>
> commit f230e80b423f6cb002015ab4771c06a53d5a2287
> ("m68k: fix memcpy to unmatched/unaligned source and dest on 68000")
>
> | The original 68000 processors cannot copy 16bit or larger quantities from
> | odd addresses. All newer members of the 68k family (including ColdFire)
> | can do this.
>
> So all Coldfires can do unaligned _reads_, but not unaligned _writes_
> (exceptions below)?

This strikes me as odd. Maybe this has been wrong all along. I need
to check further but in a little testing I did today I think it may
well be that all ColdFire support unaligned reads and writes.


>>>> I also think that the Coldfire 5272 can do unaligned accesses, but I
>>>> cannot test that at the moment.
>>
>>
>> According to the MCF5272 User Manual, "it supports misaligned data
>> accesses ...". So it looks like it does.
>>
>> Having a CONFIG_CPU_HAS_NO_UNALIGNED looks like a really good solution
>> then. We need to be able select it as required on individual CPU types.
>
> For now, I just make COLDFIRE select it, but we can move it to the individual
> CPU types later.

No matter what I find I still think this is the way to go.

Thanks
Greg


------------------------------------------------------------------------
Greg Ungerer  --  Principal Engineer        EMAIL:     gerg@...pgear.com
SnapGear Group, McAfee                      PHONE:       +61 7 3435 2888
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Milton, QLD, 4064, Australia                WEB: http://www.SnapGear.com
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