Proposal: Replace xstat (stat version dispatcher)

[Florian Weimer]

* Joseph Myers:

> On Mon, 17 Dec 2018, Florian Weimer wrote:
>
>> Should we switch this over to symbol versioning, with definitions for
>> the stat, fstat, &c functions in libc.so.6?
>
> I think we should (for both stat and mknod functions - and thus use only 
> the new mechanism for time64 variants of stat functions).

Okay, I'll look at this in late winter then.

> If the type layouts do change in future, using symbol versioning would
> be friendlier to users than the existing mechanism (it would mean
> binaries requiring the new layout reference the new symbol versions
> and so obviously need a new glibc version, rather than only failing at
> runtime because they pass a new version number to the __x* functions)
> - though as usual with such changes users may dislike building with a
> new glibc introducing requirements on a new symbol version even though
> they're only using old functions (users in such cases should be
> building using an old-glibc sysroot if they don't want new-glibc
> dependencies, but don't always do so).

We still have such a bump coming up for bug 23323, so maybe we can
tackle both in the 2.30 cycle.

Thanks,
Florian