Re: Unaligned memory explained.

Martin Ostermann (ost@comnets.rwth-aachen.de)
20 Nov 1996 10:32:24 +0100

elf@netcom.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

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