I didn't spend much time looking at it, but to me the code looks more like C than C++ lol

https://fuchsia.googlesource.com/zircon/+/master/kernel/incl... https://fuchsia.googlesource.com/zircon/+/master/kernel/kern...

Even things like SpinLock, which I was expecting to use class for RAII, looks like it was implemented using C, then with a C++ wrapper: https://fuchsia.googlesource.com/zircon/+/master/kernel/incl...

So to me (I'm no C/C++/Kernel/etc. expert) it looks like they are writing the kernel mostly in C, with C++ goodies sprinkled in some places, where it's useful (ie: RAII for spinlock guard)