[Animats]

In QNX? The boot loader loads the kernel and whatever other processes you put in the boot image. They all start as soon as the kernel starts. The kernel itself is just memory allocation, message passing, CPU dispatching, and timers. It has no I/O at all, no persistent state, and it's passive - any activity initiation has to come from user space. It doesn't even have strings.

Actual kernel debugging is rarely needed except on strange or broken hardware. If you have to do that, you use a JTAG debugger.

Further startup is handled by a startup process in the boot image. It's running in user space, and loads more drivers, file systems, networking, etc. Anything it needs to log it sends to a user space logger process that was also part of the boot image. What that does depends on the target hardware. Often, there's no console or display in embedded. It might send on a network. Or write to a circular buffer that can be read out later.