Yes, generally speaking you need inline assembly to execute whatever architecture-specific instruction is used to enter the kernel (`int 0x80`, `syscall`, `swi`

Yes, generally speaking you need inline assembly to execute whatever architecture-specific instruction is used to enter the kernel (`int 0x80`, `syscall`, `swi`, etc.). And in the kernel you need inline assembly for other various architecture-specific instructions so you can execute them as part of your regular code instead of having to write them in a separate assembly file. For the weirder cases like right after boot or handling an interrupt you generally just have to go full assembly for that, since in general you're not started out in a state where you can just start running your typical C/Rust/etc. code. It depends heavily on your platform at that point though.