Yes you can. For 32 -> 64, and assuming the OS supports both modes in the same process, this code should be sufficient: switch_to_64bit: pop

Yes you can. For 32 -> 64, and assuming the OS supports both modes in the same process, this code should be sufficient: switch_to_64bit: pop edx ;EDX=return address xor ebx,ebx ;EBX=selector .next_sel: add bx,8 ;try next jc .exit ;none found, -> segfault lar eax,bx ;load access rights jnz .next_sel ;failed? and eax,0x60F400 ;mask bits cmp eax,0x20F000 ;64bit code selector? jne .next_sel ;no .exit: or bl,3 ;set RPL to ring3 push ebx ;selector push edx ;offset retfd ;go there