How to get all dynamic printk messages on boot

Sometimes when something goes wrong during kernel boot it might be helpful to get as much info as possible on what was happening from very start right to the moment when all stopped to work.

Most of drivers and even entire kernel subsystems are well instrumented with dynamic printk messages. And this is how to enable output of all them.

1. In kernel configuration enable CONFIG_DYNAMIC_DEBUG, note it depends on CONFIG_PRINTK & CONFIG_DEBUG_FS so enable them beforehand.
2. In kernel bootargs add "dyndbg=+p".

Now boot kernel and capture very verbose console output.