The coding guidelines explicitly prohibit the use of "naked"/C-style
pointers. However, there were some prominent examples in the kapi and
the core kernel source. This changeset replaces them with the
appropriate smart pointer types.

The "X" constraint tells GCC that any operand whatsoever is valid to be
placed in the assembler template. This makes no sense in this case,
since that would allow for the exact expression to be inserted. If that
happens, which it does when `-Og` is active, GCC is unable to assemble
that template.

The correct constraint is forcing the value into a register.

A double fault is a very x86-64 specific type of exception and not
recoverable in a generalized way. Thus we should handle it internally,
with handling currently being triggering a panic, and not forward it to
the architecture-independent kernel layer.