Having been into the system call handling path myself, while working on the LX brand (Linux system call emulation), I definitely recommend this article. The writing is great, and the technical treatment is thorough and accurate.
That this (excellent, must-read) article was ignored on HN but rose to the top on lobste.rs really says it all for me; good on us all!
Offtopic (I’m still reading the article), but the fonts used are beautiful.
Author here, I purchased the fonts from Matthew Butterick. I especially enjoy using Triplicate as my monospace font.