When writing code in Assembly language, it's preferable to stick to certain calling conventions (the way parameters are passed to procedures) when invoking procedures because, first of all, this minimizes the occurrence of annoying and hard to find errors and, of course, help you link your Assembly modules to high-level languages. There are quite a few calling conventions for Intel Architecture, but we will only consider some of them, which we will use later in this book.

We already know about procedures and we have even mentioned the term "calling convention" in the previous chapter, so you may wonder why it is now that we cover the mechanism itself. The answer is quite simple--invocation of a procedure is a process that requires certain preparations, and, as such preparations would logically be the same with every procedure call, it is obvious to implement these preparations in the form of macro instruction.

First, let's see the calling conventions that we will cover in this part of the chapter: