[cxx-abi-dev] C++ ABI version 2

[Marc Glisse]

On Wed, 20 Nov 2013, John McCall wrote:

> Well, to be clear, these would be recommendations for people willing to 
> endure an ABI break.  That would still be a big NO-NO for any 
> established platforms that care about binary compatibility.
>
> And most of these changes are pretty minor improvements; the ABI has 
> really held up very well.

Indeed.

>> Maybe revisit some old issues?
>>
>> A-9 has the comment: "this won't happen often", but it affects sizeof(tuple<tuple<int>>) in libstdc++. Hmm, no, it doesn't, but it would if they swapped the order of their bases (currently for tuple<int,unsigned> they store the unsigned before the int). Of the 3 permutations tuple<int,E,E>, tuple<E,int,E> and tuple<E,E,int> where E is empty, only 1 has a small size, whereas I believe at most 1 should be large (0 would be great). And that's not the only place I've hit this.
>>
>> A-5: gcc and HP seemed to find it hard to implement at the time. Would that still be the case? (it may need to mention move constructors now)
>> I seem to be missing the detail that makes it so complicated.
>
> I am not sure how to interpret these comments.  Would you mind 
> translating them into HTML #entity references, or at least section 
> numbers, of the living document at:
>  http://mentorembedded.github.io/cxx-abi/abi.html

A-5, A-9 were references to the issue list:
http://mentorembedded.github.io/cxx-abi/cxx-closed.html#A9
(A-5 has no anchor but is easy to find)

A-5 is about section 3.1.3 #empty-parameter, where we could omit some 
empty arguments passed by value.

A-9 is about section 2.4.II.3 #class-types, where if offset 0 fails we 
don't try offset nvalign(D), 2*nvalign(D), etc but jump straight to 
dsize(C).


PS: sorry if my message has to go through moderation as a post by a 
non-member, I am receiving the emails, and I even found the message from 
when I registered, and I did use the same email address, so I don't know 
why it is complaining.

-- 
Marc Glisse