The perils of transition to 64-bit time_t
In the Overview of cross-architecture portability problems, I have dedicated a section to the problems resulting from use of 32-bit time_t type. This design decision, still affecting Gentoo systems using glibc, means that 32-bit applications will suddenly start failing in horrible ways in 2038: they will be getting -1 error instead of the current time, they won’t be able to stat() files. In one word: complete mayhem will emerge.
There is a general agreement that the way forward is to change time_t to a 64-bit type. Musl has already switched to that, glibc supports it as an option. A number of other distributions such as Debian have taken the leap and switched. Unfortunately, source-based distributions such as Gentoo don’t have it that easy. So we are still debating the issue and experimenting, trying to figure out a maximally safe upgrade path for our users.
Unfortunately, that’s nowhere near trivial. Above all, we are talking about a breaking ABI change. It’s all-or-nothing. If a library uses time_t in its API, everything linking to it needs to use the same type width. In this post, I’d like to explore the issue in detail — why is it so bad, and what we can do to make it safer.
