[Animats]

From the title, I thought this was going to be about the parts of a program that run before the main function is entered. Static objects have to be constructed. Quite a bit of code can run. Order of initialization can be a problem. What happens if you try to do I/O from a static constructor? Does that even work?

[amitprasad]

This is heavily language runtime dependent — there’s nothing that fundamentally stops you from doing anything during the phase between jumping to an entry point and the main()

[abnercoimbre]

Indeed the craziest among us occasionally abuse this fact, so long as the compiler implementation lets us.

[Animats]

Right. This tends to come up with packages, which just by virtue of being loaded, set up to do something such as log, print, catch errors, or phone home to something.