If you want to write Assembly programs for the Amiga you can either work directly on a real system or use a cross-compiler. I prefer to work on my Linux system because, as much as I like retro architectures, I also like the power of a good Unix system and a modern editor.
Cross-compiling is a very simple concept: instead of compiling source code and creating binaries for the architecture you are running the compiler on, you create binaries for a different architecture. In this case the host architecture is Linux/amd64 and the target architecture is Amiga.
As this is not the only project I am following at the moment, I created a directory to host everything I need for the Amiga development: compiler, documentation, scripts.