Messages in this thread | | | Date | Wed, 2 Feb 2011 16:24:59 -0800 | From | Dmitry Torokhov <> | Subject | Re: Early crash (was: Re: module: show version information for built-in modules in sysfs) |
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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
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