You can still use 32-bit wide addresses in 64-bit mode and sign-extend them into 64-bit registers. If you have a statically compiled binary all you need is com

You can still use 32-bit wide addresses in 64-bit mode and sign-extend them into 64-bit registers. If you have a statically compiled binary all you need is compiler support for 32-bit address mode in the otherwise 64-bit ready instruction set and on x86 you get access to more registers etc but you don't pay the price for the wider addresses stored in data structures. OTOH if you use shared libraries you also have to have your shared libraries compiled in that mode too. The difficulty of dealing with that depends also if you gave a hybrid system or a full 32 bit userspace