Re: Size and pack

[Kilgallen@SpamCop.net (Larry Kilgallen)]

In article <slrn9tqd33.c7n.lutz@belenus.iks-jena.de>, lutz@iks-jena.de (Lutz Donnerhacke) writes:
> * Larry Kilgallen wrote:
>>> Compile on Alpha and get BUS ERROR.
>>
>>Presumably that is a runtime rather than compilation time error.
> 
> Correct.
> 
>>You didn't say what model of Alpha, but older chips require
>>certain instructions be aligned.  VMS deals with this through
>>alignment fault handlers that fix up such problems at a penalty
>>of about 100 instructions.  Perhaps you are on Unix or Linux
>>(you didn't say in the body text).
> 
> OSF/1. Yep, and I added a pragma Atomic to provocate this effect.

RM C.6 10

"It is illegal to apply either an Atomic or Atomic_Components pragma
 to an object or type if the implementation cannot support the indivisible
 reads and updates required by the pragma"

The Alpha 21064, 21064A and 21164 (at least) cannot support indivisible
reads and updates of non-aligned longwords or words.

That would seem to indicate that depending on the VMS fixups would not
be allowed with pragma Atomic either.   It certainly would not produce
what I think of as being correct code for the meaning of Atomic.  Some
other poster can comment regarding the meaning of "illegal" vs. other
pejoratives with regard to error messages generated :-)