Quick but complete guide to writing proper functions in YASM x86-64 assembly on Linux. See how to pass integers, pointers & floats, return values, follow the ABI, disable C++ name mangling with extern "C", and call back and forth between C++ and assembly in a real working example.

Great for people moving from NASM/GAS or trying to mix assembly with higher-level code.

00:00 Introduction and Video Overview
00:28 What Are Functions in Programming
00:56 Why Functions Are Harder in Assembly
01:24 Topics Covered in This Video
01:59 About the Makefile and Prerequisites
02:28 Hybrid C++ and Assembly Program Plan
03:01 Using extern "C" to Disable Name Mangling
04:03 Main Driver Function in C++
05:00 Adding a Callable C++ Function for Assembly
05:42 Explaining extern "C" Placement
06:16 Assembly File Skeleton and Data Section
06:41 Creating Null-Terminated Strings
07:49 Section .text and External Symbols
08:52 Declaring my_cpp_function as extern
09:20 Defining my_assembly_function
09:40 Labels vs Real Functions
10:31 The call Instruction and Return Address
11:16 Why Jumping Instead of Calling Crashes
11:47 Global Directive for Exporting Functions
12:32 Basic Function Structure
13:20 Implementing my_assembly_function Prologue
14:50 Receiving Arguments in ABI Registers
16:30 Printing Received Integer Arguments
18:10 Handling Pointer Arguments (C Strings)
19:40 Passing Floating-Point Arguments in XMM
21:15 Printing Floats from Assembly
23:00 Calling Back to C++ Function
25:40 Preparing Arguments for my_cpp_function
27:20 Loading XMM0 and XMM1 for Floats
29:10 Making the Call to C++ Function
30:50 Receiving Double Return Value in XMM0
32:30 Saving Returned Float to Memory
34:10 Printing the Returned Value
36:00 Final Messages and Program Flow
38:20 Fixing String Pointer Crash Issue
40:00 Correcting Argument Loading
42:10 Passing String Owned by Assembly
44:00 Observing Successful Output
45:47 Saving and Restoring XMM0 Safely
47:14 Printing Final Returned Float
48:32 Importance of Following the ABI
50:29 Summary of Covered Topics
51:03 Closing Remarks and Call to Subscribe

#x86Assembly #YASM #AssemblyLanguage #x64 #LowLevelProgramming #ReverseEngineering #SystemsProgramming #LinuxDev #ABI #CPlusPlus

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