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Re: unaligned accesses

On Wed, Jul 24, 2002 at 02:57:21PM -0400, Thomas Evans wrote:
> The most prevalent architecture for Linux doesn't
> have an issue with unaligned accesses, so most developers
> are unaware. (Yes I know the most prevalent Linux architecture
> benefits greatly from aligned accesses, but unaligned ones are handled
> transparently and hence ignored).

Well, AFAIK, the transparency on Intel processors is *hardware*
transparency - there's no notification that it has happened, and
the *hardware* does the (slow) fixup.

On Alpha, "transparency" can be achieved by deleting the message
print, but the hardware will still trap into the kernel to get the
access fixed up via software.

Because of the (probable) order of magnitude more work on Alpha to
deal with unaligned accesses, it's always been our policy to report
their occurrences, though one will only see sporadic messages (I think
it is 4 every so many seconds, or 4 out of every som many, or some
such scheme). The reports are meant to strongly encourage the fixing
of the offending code, which will benefit all architectures.


Jay A Estabrook                            HPTC - LINUX support
Hewlett-Packard Company - MRO1-2/K15       (508) 467-2080
200 Forest Street, Marlboro MA 01752       Jay.Estabrook@hp.com

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