[cxx-abi-dev] What is a POD? TC1 or first C++ Standard

[Nathan Sidwell]

Mark Mitchell wrote:
> Dennis Handly wrote:
> 
>>> GCC is not going to change back to the pre-TC1 definition, even for
>>> return values
>>>   
>>
>>
>> What do you mean by "return values"?  I said it only affects layout.
>> I first thought it also affects them but 3.1.4 Return Values, says 
>> nothing
>> about PODs.
>>  
>>
> You are correct.  I thought it said that non-PODs could not be 
> passed/returned in registers, but, in fact, it is more specific: it 
> talks about non-trivial copy constructors and destructors.
> 
> That makes things somewhat simpler.
> 
> It seems to me that a POD with a pointer-to-member data member should 
> not be a "POD for purpose of layout" because the layout of a "POD for 
> the purpose of layout" is supposed to be whatever the C ABI would 
> require -- and the C ABI does not specify the layout of a type 
> containing a pointer-to-member.
> 
> Now, the question is, when would this make a difference?  Dennis, can 
> you post a small test case showing where the layout is different 
> depending on whether you use the TC1 or pre-TC1 definition of POD?
> 
I would have thought it'd change when the tail padding of such a class could
be used by a derived class. Something like,

struct A {
   int A::*ptr;
   char f;
};

struct B : A {
   char g;
};

Where is B::g placed?

nathan

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