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

Dmitry Torokhov
2011-02-03T00:24:59Z

On Wed, Feb 02, 2011 at 04:10:04PM -0800, Andreas Schwab wrote:
> Dmitry Torokhov <dtor@vmware.com> 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.

Thanks,
Dmitry