Why does -Wabi-tag complain when -std=c++03?

[Jonathan Wakely]

On 24 March 2016 at 16:43, Jeffrey Walton wrote:
> There are lots of folks who have experienced the issue; check out
> http://bugs.debian.org/cgi-bin/pkgreport.cgi?tag=libstdc%2B%2B-cxx11;users=debian-gcc@lists.debian.org.
> Debian happened to say "f**k it, we'll just recompile everything under
> the new ABI and be done with it". But they experienced the corner-case
> issues too. I don't know why they did not consult with the GCC folks.

They did. Rebuilding everything is the right choice. For Debian to
modify all their libraries to use a "dual ABI" and ship those modified
versions would take months, probably years, and would require ongoing
maintenance as the modified versions diverge from upstream.

> I'm the type of person who wants to get a definitive or authoritative
> answer so I can make informed decisions. That's why I come here to ask
> the experts.
>
> This step was not obvious to me at all. I don't ever recall having to
> define a library macro for a library:
>
>     $ g++ -D_GLIBCXX_USE_CXX11_ABI=0 -c test.cxx -o test-v1.o
>     $ g++ -D_GLIBCXX_USE_CXX11_ABI=1 -c test.cxx -o test-v2.o
>
> Naively, because of the blog post on the coexistent implementations, I
> was looking for an option like -dual-abi to do it for me.

Which is a leap that doesn't in any way follow from a literal reading
of the blog post!