Update (28th of September 2026) Max Desiatov told me that the @c swift attribute should work, instead of declaring the functions using @_cdecl. The @c attribute marks a global function as a C function implemented in Swift, which formalizes the @_cdecl attribute. A link to the proposal is available here. I did update the blog post and the code accordingly to that comment. Thanks Max! I started a small experiment: writing a very basic kernel in Swift, and running on QEMU.