Re: Early crash (was: Re: module: show version information forbuilt-in modules in sysfs)

[Dmitry Torokhov]

On Wed, Feb 02, 2011 at 04:24:59PM -0800, Dmitry Torokhov wrote:
> On Wed, Feb 02, 2011 at 04:10:04PM -0800, Andreas Schwab wrote:
> > Dmitry Torokhov <dtor@xxxxxxxxxx> writes:
> > 
> > > Even pointers? I'd expect pointers to be aligned on 4-bytes boundaries?
> > 
> > Pointers are not special in any way.  Why should they?  On the machine
> > level pointers are just numbers.
> 
> Are pointers (along with ints/longs) on m68k naturally aligned on word
> boundary even though they are 32 bit?
> 
> Anyway, here is the description that introduced alignment statement:
> 
> commit 02dba5c6439cff34936460b95cd1ba42b370f345
> Author: ak <ak>
> Date:   Sat Jun 21 16:18:16 2003 +0000
> 
>     [PATCH] Fix over-alignment problem on x86-64
> 
>     Thanks to Jan Hubicka who suggested this fix.
> 
>     The problem seems to be that gcc generates a 32byte alignment for static
>     objects > 32bytes.  This causes gas to set a high alignment on the
>     section, which causes the uneven (not multiple of sizeof(struct
>     kernel_param)) section size.  The pointer division with a base not being
>     a multiple of sizeof(*ptr) then causes the invalid result.
> 
>     This just forces a small alignment, which makes the section end come out
>     with the correct alignment.
> 
>     The only mystery left is why ld chose a 16 byte padding instead of
>     32byte.
> 
>     BKrev: 3ef485487jZN-h3PtASDeL2Vs55NIg
> 
> 
> I guess this does not directly apply to modversions since they are
> currently under 32 bytes, but I wonder what happen if we decide to
> extend one of the structures involved...
> 
> I guess explicitly setting alignment requirement for struct
> module_version_attribute is the best option.
> 

So here is the patch that explicitly specifies alignment for struct
module_version_attribute. I tested it on i386 and x86_64 and I believe
it will fix the issue with m68k but I do not have access to such a box.

Thanks,
Dmitry