Lecture Notes: Assembly Language Function Prologue

Introduction

• Focus on assembly code, specifically AT&T syntax.
• Example function: add which takes two arguments and returns their sum.

Function Calls in Assembly

• Arguments are pushed onto the stack from right to left.
• Return address is also pushed onto the stack when a function is called.
• ESP (Stack Pointer) always points to the top of the stack.
• High memory addresses are at the top of the stack, low memory addresses are at the bottom.

Analyzing the Prologue

1. Line 1: push EBP

   • Pushes the current value of EBP onto the stack.
   • This is referred to as old EBP, which is the value of EBP before the function execution.
   • ESP moves down to point to the new top of the stack (where old EBP is now stored).

2. Line 2: mov ESP, EBP

   • Moves the value that ESP is pointing to into EBP.
   • Essentially, EBP will now point to the same location as ESP.

Importance of the Prologue

• The prologue is crucial for setting up the stack for function calls.
• It prepares the necessary references for local variables and maintaining the function call structure.
• The prologue consists of:
  • Pushing the old EBP onto the stack.
  • Setting the new EBP to the current ESP.

Conclusion

• The prologue is essential for stack management in assembly functions.
• Future topics will cover the significance of the prologue and stack management in more detail.