Rust programs don't start at main. Before the first line of user code runs, the linker, the platform loader, and a set of platform-specific initialization hooks have already done substantial work. Matt Mastracci maintains ctor, link-section, and scattered-collect crates that let Rust code register both work and data in custom link sections and run it before main across Linux, macOS, Windows, and WASM. This session walks through building a link-time hashmap, what actually happens during that window, why each platform gets there differently, and where the abstractions leak... including the provenance and LTO failures that only appear once optimizers get involved.
