We have seen the most general techniques for debugging the Linux kernel. However, some special scenarios require the use of different methods. One of the most common scenarios in embedded Linux development is the debugging of the booting process. This recipe will explain some of the techniques used to debug the kernel's booting process.
A kernel crashing on boot usually provides no output whatsoever on the console. As daunting as that may seem, there are techniques we can use to extract debug information. Early crashes usually happen before the serial console has been initialized, so even if there were log messages, we would not see them. The first thing we will show is how to enable early log messages that do not need the serial driver.
In case that is not enough, we will also show techniques to access the log buffer in memory.