Re: time64 / Large File Support: 2) default time64 breaks legacy 32bit binaries

[Florian Weimer <fweimer@redhat.com>]

* Andreas K. Huettel via Libc-alpha:

> This was discussed already in the previous thread on this list [1],
> with reactions ranging from "need new triplet" via "need new libdir"
> to "meh".  The latter is a bit surprising given how much emphasis
> glibc usually places on backwards compatibility.

> [1] https://sourceware.org/pipermail/libc-alpha/2022-November/143386.html

For me, it's ”meh” because for our distributions, we need to keep time_t
at 32 bits.  We don't want to allocate resources to make all core
libraries dual-time_t, like it was contributed to glibc.  But such a
dual-ABI nature would be a prerequisite for offering libraries that
support 64-bit time_t.  It really has to be in addition to 32-bit
time_t.

In my world, 32-bit support is for running binaries built with GCC 2.95.
(Some of them built decades ago, some of them new.)  Fedora also used to
have a 32-bit time_t use case for Wine, but I think that is rapidly
going away, with Wine transitioning to a different technology for
running 32-bit applications (the dependency is purely in the
implementation of Wine).

I expect that our ABI compatibility requirement will go away in the
second half of 2024.  Until then, it puts us in conflict with certain
64-bit time_t approaches suggested by the community.  I still hope that
we can eliminate the requirement sooner, so that I don't have to argue
against those approaches, but these kind of decisions are hard.  I
really wish we could avoid this conflict.

> While we could certainly go ahead and invent a solution in Gentoo here, this
> makes no sense at all for one distribution alone. This is an upstream problem
> and should be solved here... pretty please? opinions?

There's some risk that several key upstreams will tell us, “just rebuild
everything with time_t as 64-bit”, at which point we would have to come
up with a custom, downstream-only ABI that has dual time_t support.

And I don't think glibc is the upstream project you need to work with
here.

Thanks,
Florian