For common programs it's not very difficult, usually just recompile. But if it uses assembly then you are out of luck. Also if it requires a library that uses i

For common programs it's not very difficult, usually just recompile. But if it uses assembly then you are out of luck. Also if it requires a library that uses it. For an OS it is different, you need to reimplement many parts: bootloader, drivers, task scheduler, virtual memory...