Search notes:

boot process

arch/x86/boot/header.S (start_of_setup:)
arch/x86/boot/main.c (main)
arch/x86/boot/compressed/head_64.S (startup_64, or startup_32?)
arch/x86/boot/compressed/misc.c (decompress_kernel)
init/main.c (start_kernel())

Log files

Messages and errors occuring during the boot process are written into /var/log/boot.log. Other messages are written to /var/log/dmesg.

See also

Apparently, /etc and /usr is needed in the boot process. Thus, they need to be in the root partition.
booting Linux
Booting a PC

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