[U-Boot] 32-bit OS on 64-bit core

[Robert Thorhuus]

Hello!

I hope you all can help me with understanding.

Some (all?) PowerPC implementations have a bit in the MSR to tell the core to run in either 32 bit or 64 bit mode. At least my core "in front of me" has this. It is a 64 bit implementation and I need to be able to boot both 32/64 bit OSes (with same U-Boot).

My initial hope was that 32 bit programs would run in 64 bit mode. This to ease up my U-Boot implementation. And as far as I know you do not change the bootloader when you switch between a 32 bit OS and a 64 bit OS on your PC?! But of course that bit in the MSR is there for a reason :)

So, my guess how to solve this is that bootloaders are usually 32 bit to be backward compatible and let the OS decide to step up to 64-bit or not. Is this true and the general rule? 

But I feel there are occassions when a 64 bit bootloader is nice, to access more memory at once for instance. 
Do you have any recommendations for me?

Thanks
BR
Robert