Re: [PATCH] m68k: Use generic strncpy_from_user(), strlen_user(), and strnlen_user()

Greg Ungerer
2012-06-06T06:35:53Z

Hi Geert,

On 06/06/12 06:57, Geert Uytterhoeven wrote:
> On Wed, May 30, 2012 at 4:04 PM, Philippe De Muyter<phdm@macqel.be> wrote:
>> On Wed, May 30, 2012 at 01:20:02PM +0200, Geert Uytterhoeven wrote:
>>> On Wed, May 30, 2012 at 12:22 PM, Philippe De Muyter<phdm@macqel.be> wrote:
>>>> On Tue, May 29, 2012 at 11:33:36PM +0200, Geert Uytterhoeven wrote:
>>>>> Signed-off-by: Geert Uytterhoeven<geert@linux-m68k.org>
>>>>> ---
>>>>> Do we also want
>>>>>
>>>>> select HAVE_EFFICIENT_UNALIGNED_ACCESS if (!COLDFIRE&& !M68000)
>>>>
>>>> Sorry, I did not follow what happened to unaligned accesses, but
>>>> CPU32 family (at least 68340) crashes on unaligned accesses.
>>>
>>> We don't seem to have CONFIG_M68340 in arch/m68k/Kconfig.cpu?
>>
>> I have a local port here (but based on an ancient linux kernel, 2.6.2 IIRC)
>>
>>> But Freescale's website confirms both 68340 and 68360 are CPU32.
>>>
>>> arch/m68k/include/asm/unaligned.h assumes CPU32 (CONFIG_MCPU32)
>>> can do unaligned accesses:
>>
>> That's not true. Accessing a 16- or 32-bit word at an odd address
>> with a 68340 generates an Address Error Exception. I remember
>> discovering a bug in the ppp kernel code because of that.
>>
>>>
>>> #if defined(CONFIG_COLDFIRE) || defined(CONFIG_M68000)
>>> #include<linux/unaligned/be_struct.h>
>>> #include<linux/unaligned/le_byteshift.h>
>>> #include<linux/unaligned/generic.h>
>>>
>>> #define get_unaligned __get_unaligned_be
>>> #define put_unaligned __put_unaligned_be
>>>
>>> #else
>>> /*
>>> * The m68k can do unaligned accesses itself.
>>> */
>>> #include<linux/unaligned/access_ok.h>
>>> #include<linux/unaligned/generic.h>
>>>
>>> #define get_unaligned __get_unaligned_be
>>> #define put_unaligned __put_unaligned_be
>>>
>>> #endif
>>>
>>> Is this wrong?
>>
>> I can't tell from reading just the lines above, but I think one should add
>> "|| defined(CONFIG_MCPU32)" at the end of the if condition.
>
> Greg?
>
> If more CPUs cannot handle unaligned accesses, I propose to add
> CONFIG_CPU_HAS_NO_UNALIGNED.

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.

>> 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.

Regards
Greg

------------------------------------------------------------------------
Greg Ungerer -- Principal Engineer EMAIL: gerg@snapgear.com
SnapGear Group, McAfee PHONE: +61 7 3435 2888
8 Gardner Close FAX: +61 7 3217 5323
Milton, QLD, 4064, Australia WEB: http://www.SnapGear.com