The Rust Calling Convention We Deserve · mcyoung
I will often say that the so-called “C ABI” is a very bad one, and a relatively unimaginative one when it comes to passing complicated types effectively. A lot of people ask me “ok, what would you use instead”, and I just point them to the Go register ABI, but it seems most people have trouble filling in the gaps of what I mean. This article explains what I mean in detail.
I have discussed calling conventions in the past, but as a reminder: the calling convention is the part of the ABI that concerns itself with how to pass arguments to and from a function, and how to actually call a function. This includes which registers arguments go in, which registers values are returned out of, what function prologues/epilogues look like, how unwinding works, etc.
This particular post is primarily about x86, but I intend to be reasonably generic (so that what I’ve written applies just as well to ARM, RISC-V, etc). I will assume a general familiarity with x86 assembly, LLVM IR, and Rust (but not rustc’s internals).
