1.2 ops.rs - Operators

The operations are defined as a trait in jit/ops.rs. They are sysv64 extern functions. In the JIT, we put their memory addresses in the rax register and call rax.

The actual implementation of the functions is on the Context struct. They mostly operate on the Context, and in the case of a large number of such operations, this helps to keep their implementation organized.

So the JIT function makes calls to functions in our Rust code. The operations are implemented by taking a pointer to Context as the first argument, and the other arguments can come from destructuring the enum.

For example, when building the JIT, Operator::Exit(30.0) will be translated to a function call:

Ops::op_exit as extern "sysv64" fn(&mut Context, f32)

Before the function call, in the JIT we will have to arrange argument values in the CPU registers and the stack, according to the conventions of the CPU hardware and how the OS uses that CPU.

We tag the extern function with the ABI we are using in the JIT. Here we are using sysv64 (System V AMD64 ABI) which is the expected on Linux and Mac, but Rust will compile it accordingly on Windows as well.

So far this was easy. When writing the JIT, there will be a wee bit more documentation-digging.