And I chose rust at random because its an available systems language. Why not something else? You don't actually need C at the bottom layer. It won because the OS are most commonly written in C, it's encountered elsewhere and therefore popular. Usually because it helps get the desired result. That isn’t nothing either.

In days of olde there was pascal calling convention. Why? The os was written to that, because it was written in that. Surprise! I'm not even suggesting these are bad things.

Linux for me is a kernel. The choice of C is purely an implementation detail based on pragmatic decisions to suit its purpose. I am merely suggesting that the calling convention isn’t locked at all layers for all time. Yes you need a common convention. But it needn't be C and it doesn't need to be C all the way up or down either.

I'll leave it there. Seems that discussing this kind of thing isn't wanted.

Side note: I wonder what would have happened if I'd chosen Lua for my example. Would people have gotten hung up on the fact that its commonly implemented in C? Would they have locked onto that yet not realised that it needn't actually be written in C at all? If you wish to explore that, swap rust for lua in my previous comment. There are ways of using lua as a calling convention without even referencing C. If you want a more realistic example, swap in dart or more likely D. Everything I've said still applies. And yes you can have mutliple calling conventions or even a simpler one. Its just a convention of how to pass parameters, amongst other things. Thats basically it.