In x64, the calling convention is more dependent on the registers. For Windows, the caller function passes the first four arguments to the registers in this order: rcx, rdx, r8, r9, and the rest are pushed back to the stack. While for the other operating systems, the first six arguments are usually passed to the registers in this order: rdi, rsi, rdx, rcx, r8, r9, and the remaining to the stack.
In both cases, the called function cleans the stack after using ret imm, and this is the only way to clean up stack for these operating systems in x64.
