[Python-Dev] GC head alignment issue

[Guido van Rossum]

> I have anuther issue with the change tho: as written, it forces
> the struct (it's only a union by accident) _gc_head to be aligned,
> but is it obvious that it really has to pad up the size too ?

Yes.

> If for example sizeof (int) is 4, sizeof (struct *) is 8 and
> sizeof (double) is 16, with 8 byte alignment required for doubles,
> would a compiler be allowed to make sizeof (struct _gc_head[1]) 24,
> while still keeping sizeof (struct _gc_head) at 20 ?

No.  Each item in an array has to be aligned, so the sizeof a struct
must be a multiple of the largest required alignment for any of its
items.  It's all spelled out in the C standard, so don't worry.

--Guido van Rossum (home page: http://www.python.org/~guido/)