Sure, in those cases we emit calls to C functions. The only thing we need to know is what registers are taken as input, what registers are output and what regis

Sure, in those cases we emit calls to C functions. The only thing we need to know is what registers are taken as input, what registers are output and what registers are preserved. In QEMU parlance, these are helper functions, and they have actual implementations. But for decompilation purposes, you don't need to implement them. You just need to know how they interact with the registers.