The verified down to the machine code and GPLed seL4 is only 9,000 line, and some of those are largely artifacts of the hand translation from Haskell to C. On

The verified down to the machine code and GPLed seL4 is only 9,000 line, and some of those are largely artifacts of the hand translation from Haskell to C. On the other hand, it doesn't do all that much for you, there's a lot of kernel type behavior you have to implement above it. But you are starting out with a relatively very small Trusted Computing Base (TCB).