Re: Objective C and STRUCTURE_SIZE_BOUNDARY

[Ovidiu Predescu <ovidiu at cup dot hp dot com>]

On Fri, 28 May 1999 17:45:17 +0100, Philip Blundell <pb@nexus.co.uk> wrote:

> >with the same structure boundary size? How this works? Is there a way to find
> >out at runtime what was the option passed to the compiler at the build time?
> 
> No.  What I was thinking we could do to fix this was introduce a new constant, 
> call it MAX_STRUCTURE_SIZE_BOUNDARY, that is set to the upper bound you can 
> have on STRUCTURE_SIZE_BOUNDARY.  I think this should cause Objective C to 
> always use the more cautious alignment (ie align to 32-bit boundaries) which 
> will work regardless of what user code is doing.

I'm not sure I understand your statement. The Objective-C runtime library uses
that value to determine how to dynamically access structure members. If such a
structure is part of another structure then depending on the compiler option,
the ObjC runtime could try to access it aligned at either 8 or 32 bits. If we
use a 32-bit boundary, we could be wrong when the user code is compiled with a
8-bit boundary.

Ovidiu