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

[Greg Ungerer]

Hi Geert,

On 06/06/12 06:57, Geert Uytterhoeven wrote:
> On Wed, May 30, 2012 at 4:04 PM, Philippe De Muyter<phdm@xxxxxxxxx>  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@xxxxxxxxx>  wrote:
> > > > On Tue, May 29, 2012 at 11:33:36PM +0200, Geert Uytterhoeven wrote:
> > > > > Signed-off-by: Geert Uytterhoeven<geert@xxxxxxxxxxxxxx>
> > > > > ---
> > > > > 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@xxxxxxxxxxxx
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
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