A problem with percpu variable cpu_number

Hi : At the beginning of start_kernel() -- init/main.c boot_cpu_init() is called and in boot_cpu_init() will call smp_processor_id() it's a macro and it will be expanded as (percpu_read(cpu_number)) and so on but i noticed that it's before setup_per_cpu_areas() in start_kernel() is that mean the percpu areas hadn't be initialized yet but why smp_processor_id() could be called before setup_per_cpu_areas() Thank you. --------------- jiangtao