System calls, FFI, and cross-platform abstractions
We’ll implement a very basic syscall for the three architectures: BSD/macOS, Linux, and Windows. We’ll also see how this is implemented in three levels of abstraction.
The syscall we’ll implement is the one used when we write something to the standard output (stdout) since that is such a common operation and it’s interesting to see how it really works.
We’ll start off by looking at the lowest level of abstraction we can use to make system calls and build our understanding of them from the ground up.
The lowest level of abstraction
The lowest level of abstraction is to write what is often referred to as a “raw” syscall. A raw syscall is one that bypasses the OS-provided library for making syscalls and instead relies on the OS having a stable syscall ABI. A stable syscall ABI means it guarantees that if you put the right data in certain registers and call a specific CPU instruction...
