Early kernel debugging
Currently it is difficult to analyze failures in early stages of the kernel. The output devices are usually initialized in arch_post_mm_init() or arch_post_smp_init(). This is quite late. Often the most critical part of kernel initialization is the memory management init, yet at this stage no output is available.
Whenever I need to debug problems with MM initialization, I need to tediously add debug output messages by hand (via a specialized debug output routine).
This is a waste of time. Instead somehow it should be possible to enable early debug messages (that go to a real output devices, such as a serial console, not just to a kernel buffer).
While in a simulator it is possible to inspect the klog, this does not work on a real machine.
If it is not possible or advisable to initialize the full output-device machinery in such an early stage, there should be a simple debug-output mechanism added for each platform.