Getting rid of alignment faults in userspace

Andy Green at
Fri Jun 17 13:11:52 UTC 2011

On 06/17/2011 01:10 PM, Somebody in the thread at some point said:

Hi -

> I've recently become aware that a few packages are causing alignment
> faults on ARM, and are relying on the alignment fixup emulation code in
> the kernel in order to work.

Just a FYI a lot of later ARM chips are solving alignment fixups in 
hardware in the Bus Interface Unit, so the problems won't show up in 
kernel stats.

> Such faults are very expensive in terms of CPU cycles, and can generally
> only result from wrong code (for example, C/C++ code which violates the
> relevant language standards, assembler which makes invalid assumptions,
> or functions called with misaligned pointers due to other bugs).

Agreed it's usually evidence of something broken and / or evil in the code.

There is still going to be a small cost even in hardware fixup so this 
is very much worth solving despite it's "becoming invisible" because the 
chips are hiding / solving it already.


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