go build -gcflags='all=-N -l' -buildmode=plugin -o ./plugins/my-printer/my-printer.so ./plugins/my-printer/
We need the flag -gcflags='all=-N -l' to allow debugging (details here)
When we run the main application we also need to add -gcflags='all=-N -l':
go run -gcflags='all=-N -l' main.go
Note: The plugins have to be build from inside the main application. Otherwise a "plugin versions do not match" error will be given when trying to open the .so file. More here