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Re: Future of libio vtable compatibility
* Carlos O'Donell:
> On 06/15/2018 03:50 AM, Florian Weimer wrote:
>> Should we instead remove the compatibility logic altogether?
>
> The libio vtable internal ABI compatibility has been a real source
> of pain over the years, and it has prevented the general cleanup
> of the libio code.
> I'm inclined to argue that glibc 2.x should remain compatible with
> the old internal ABI of the vtables, but that perhaps a future glibc
> with a new major version might drop it entirely.
But how do we test this? We learned about the incompatibility only
because there's an unambiguous error message about it. Remember that
none of the affected people tried to report this upstream. The two
internal cases we had end up with the users upgrading their obsolete
binaries anyway (we didn't get the binaries that reproduced the
issue).
It almost looks to me as if nobody really wants that level of
backwards compatibility.
We could require that vtable compatibility requires setting an
environment variable in glibc 2.28. This might finally allow us to
gather some data. Either nobody needs backwards compatibility, or our
backwards compatibility is just too perfect. It's difficult to tell
why we don't see more bug reports in this area.