Re: Unaligned memory explained.
Martin Ostermann (firstname.lastname@example.org)
20 Nov 1996 10:32:24 +0100
email@example.com (Marc Singer) writes:
> > You don't have to worry about the unaligned memory errors. They
> > have something do do with the way the alpha uses memory (could some
> > one please go over this in detail).
[good explainations ommited]
> "Why is this all-of-a-sudden a problem?" you ask. The x86 performs
> unaligned memory accesses by reading twice and fixing the result.
> It's not efficient and is usually optimized out of good programs, but
> since the x86 permits this behavior the programmers who were not
> careful about aligning their data will find their programs faulting on
> RISC machines.
I'd like to add:
The reason we don't have to worry badly about it is that on
Linux/Axp the OS catches the traps caused by this fault, and it is
emulating the above behaviour, e.g. the program will be executed
slowly, but correctly.
Martin Ostermann | mailto:firstname.lastname@example.org
Communication Networks | http://www.comnets.rwth-aachen.de/~ost
Aachen University of Technology | phoneto:++49/241/807917
Germany | faxto:++49/241/8890378
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