Comment by hackermailman

CS:APP 3rd (64bit) edition http://csapp.cs.cmu.edu/

Lectures for it are here: https://scs.hosted.panopto.com/Panopto/Pages/Sessions/List.a...

This teaches you C, x86-64 arch, stuff like two's complement integers and floating point, how memory and CPUs work, how the C compiler works (linking stage, preprocessor), and how to write/understand signals and processes, file I/O, network code ect.

After that you can just start reading the OpenBSD code and will figure it out or get an Andrew S Tanenbaum book on Operating Systems.

Note, if you buy the Pearson Global Edition of CS:APP (it's only 10% the reg price) there's a lot of errata you will have to check. I once got stuck reversing an assembly program into C that did an even/odd parity check because of a print error returning the final XOR'd value & 0 instead of & 1.