[M3devel] Target.Allow_packed_byte_aligned const or var per target?

[Rodney M. Bates]

Hmm, this sounds like a mechanism we had a discussion of several years ago.
I don't remember how it ended, but I think there was a general consensus that
it was an idea with some unresolved problems.

However, one big class of use cases for packing things is to make it possible
to define a record layout that matches one already specified externally,  a network
protocol packet, for example.  We had a much bigger problem with that regarding
different endianness, which we never did anything about.  I have some unimplemented
notes somewhere on how to do opposite-endian record layout.  It was mind-boggling,
to put it gently, and left me even more negative on so-called "little endian" than
previously.

Anyway, this is where different rules for different records on the same target
may be wanted.

On 09/20/2015 03:41 PM, Jay K wrote:
> containsLazyAlignments
>
> m3front/Module.m3:
>
> PROCEDURE SetLazyAlignment (on: BOOLEAN) =
>    BEGIN
>      IF curModule # NIL THEN
>        curModule.lazyAligned := on;
>        IF on THEN
>          curModule.containsLazyAlignments := TRUE;
>        END;
>      END;
>    END SetLazyAlignment;
>
>
> PROCEDURE Compile (t: T) =
>    VAR save: T;  zz: Scope.T;  yy: Revelation.Set;
>    BEGIN
>      (* ETimer.Push (M3Timers.emit); *)
>      Target.Allow_packed_byte_aligned := t.containsLazyAlignments;
>
>
> This feels wrong.
> Surely, Allow_packed_byte_aligned should be constant for any given target?
> Surely a pragma cannot change a target's characteristics?
> Or, rather, I found this by changing it to a constant false for all targets.
>
>
>   - Jay
>
>
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-- 
Rodney Bates
rodney.m.bates at acm.org