g++.dg/ext/packed3.C

[Nathan Sidwell]

Jan Beulich wrote:
> This test contains three invocations of Ref(), but only two of them are
> considered ill. What I'd like to get an explanation for is why the third
> (middle) instance is considered correct. After all, the u member of
> Packed is packed, and hence all the members of Unpacked in that context
> are, too. Namely, even if the object referenced by p is properly
> aligned, p.u isn't and hence p.u.i isn't either.
> 
> I'm asking this because for *-*-netware*, which uses packed structures
> by default, this test fails with an error message like the ones expected
> on the other two calls to Ref().

Although Unpacked is a pod type, if it contained non-static member functions, 
those member functions would expect a this pointer that is correctly aligned. 
We have two options
1) don't pack fields of structure type
2) don't pack fields of non-pod or non-static member function containing structs

#2 means the alignment of your field can change, depending on whether the 
field's type contains a non-static member or not.  C++ has no term for such a class.

#1) breaks GNU C compatibility, I think.

I'm not sure what the best answer is here.

If your system packs structs by default, you should not be getting the warning 
on any of the uses.

nathan

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