The syscall/errno stuff has always seemed unusual, inelegant, and inefficient --- instead of just returning a negative error code directly, the function returns the vague "an error has occurred" -1, and you have to then check errno separately after that. It only adds insult to injury when you realise that the kernel itself isn't doing it, but the syscall wrappers. And thanks to POSIX standardising this mechanism, the alternative will likely never get much adoption; of course, if you write your own syscall wrappers like this article, then you can skip that bloat.

For now this guide is linux-only, but I will be writing a windows version when I feel like firing up a virtual machine.

Unfortunately the Windows syscalls are not officially documented and even less stable than on Linux, changing even between service packs.

http://j00ru.vexillium.org/ntapi/

http://j00ru.vexillium.org/ntapi_64/

At least on Linux the first few (i.e. the oldest, most common and useful) syscalls have not really moved around over the years:

https://filippo.io/linux-syscall-table/