x86_64: long mode -> compatibility mode -> protected mode

[wshin]

Hello,

In x86_64, how would one go about writing kernel code that takes the kernel down to compatibility mode, then to protected mode, run some code and come back up to long mode?

Thank you,

[Rubberman]

And you need to do this why?

In any case, it would require some gnarly assembly code, and have tonnes of side effects that would likely cause kernel problems unless you are VERY careful to disable all the appropriate interrupts while performing the operation. Staying in that state too long will have all sorts of bad effects.