A Few Tricks to Make Life Easier

Objectives

1. Understand the include statement for NASM
2. Understand basic (leaf) function calls.

Notes

• I am tired of typing the constants over and over again.
  • A standard programming trick is include.
  • NASM supports this.
  • See Chapter 5 of the NASM manual
• %include "filename" (section 5.8.1 of the manual)
• guards

  • %ifndef SOME_LABEL
    %define SOME_LABEL
    ;code
    %endif
            

• See CONSTANTS.h
• Function Calls : Basics
  • Functions and function calls will be a issue for us all semester.
  • But I really want to use a function for printing numbers in the next code
  • So let's do a simple intro
    • We will not do things completely right here,
    • But it will work for now.
  • We can't use a jump because we don't know where to jump back to.
  • We use call function_label
  • When done we use ret
  • We will pass parameters the right way (rsi, rdi)
  • see memory.asm
• We may need to manage the stack
  • push rbp ; save the base pointer
  • move rbp, rsp ; make the current stack pointer the base pointer.
  • sub rsp,8 ; make the stack 16 bit alligned.
• Once we are done, we need to reverse this process
  • We don't need to add to rsp, as we will be "clobbering it"
  • mov rsp, rbp ; restore the stack pointer
  • pop rbp ; restore the base pointer
  • ret ; return to the calling function