At 14:31 25/01/01 +0000, Nicholas Clark wrote:
>On Thu, Jan 25, 2001 at 12:48:10PM +0000, Michael Nonweiler wrote:
> > I am worried about remaining problems with unaligned accesses to word and
> > short data.
>
>Have you experimented yet with a conventional ARM Linux setup where you
>recompile a kernel with the alignment trap handler turned on?
>You shuld be able casts in C to manufacture unaligned pointers to trigger
>the traps (IIRC it reports usage in /proc somewhere) and see if it correctly
>fixes up the results of unaligned pointer reads and writes.
>If the alignment trap handler works (in user space?) what classes of remaining
>problems are you worried about?
I am worried that the alignment trap handler doesn't work efficiently
enough, so I want to know how much it is used in a real systems. It is
_very_ slow, (100s of cycles?) so while I accept it fixes exactly the
problem I'm worried about, I want to know how frequently (both statically
and dynamically) it is used.
Your comments suggest you have never had a problem with this?
I believe existing ARM Linux setups make more use of the alignment trap
than absolutely necessary, because they allow the compiler increase
alignment assumptions by optimising accesses to structures that contain
only bytes. This is why I want to base my experiments on a non-standard
system.
Thanks,
Michael.
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