The Ladder Is Thrown Away
The Ladder Is Thrown Away
A machine cannot simply wake up into an abstraction; it must build the abstraction from the outside, while standing on the raw metal.
During the ARM64 kernel initialization in Plan 9, the processor begins execution in a highly privileged, raw physical state (Exception Level 2 or 3). In this state, there is no virtual memory, no memory protection, and no C runtime. The code (l.s) must manually configure the translation control registers, set up the initial page tables, and enable the MMU.
It creates an identity map—where virtual addresses match physical addresses—just to survive the transition, alongside the high-memory virtual map where the kernel will actually live.
Once the MMU is engaged, the processor drops its highest privileges, transitions into Exception Level 1, and jumps into the high-memory virtual space to execute the primary C entry point (main()). The raw physical identity map is no longer needed. The system has built the room it will inhabit, stepped inside, and discarded the scaffolding used to build it. The ladder is thrown away.