Gain insights into using GDB for debugging in Linux. Explore disassembly, memory investigation, and register updates. Learn about pointers, stack, and function parameters in x64 architecture.

gdb.tar.gz

C2-LA

C4-L2

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test

GNU Debugger (GDB) is used for debugging C/C++ programs in LINUX/UNIX environments. It is a good tool to investigate what is happening inside a program, and how the contents inside the memory are changed with the execution of the program.

The main focus of the course is the disassembly of the program, where we'll use simple operations in C. With the help of GDB, we'll examine the contents of the registers and memory. We'll also learn how they are changed while executing basic operations. We’ll then explore the use of pointers, stack, and function parameters, and analyze how different registers update their values. With the help of disassembly output, we’ll learn how a simple C program can be reconstructed. The disassembly output is important for debugging and core dump analysis. We’ll use assembly language for x64 architecture.

By the end of this course, you should be able to debug the programs and memory contents at assembly level when a program executes or probe into the problem when a program crashes.

Debugging, Disassembly & Reversing in Linux for x64 Architecture

# Increment and decrement numbers

In pseudocode, incrementing  or decrementing the number stored in location (address) `a` looks very simple:

```s
(a) + 1 -> (a)
(a) – 1 -> (a)
```

## Increment and decrement in C and C++ 

In C and C++, we can increment and decrement in three different ways:


# Increment
a = a + 1;
++a;
a++;

# Decrement
b = b – 1;
--b;
b--;

## Increment and decrement in assembly language
In assembly language, we use instructions `INC` and `DEC` and write:


We use `incl` when we need to specify a $32$-bit memory cell, because whether the cell is $32$-bit or $64$-bit is ambiguous when we use `a`. However, using `%eax` implies the use of $32$-bit values, so `inc` is unambiguous.

## Increment and decrement in GDB disassembly
In the GDB disassembly output, we can see the same instruction:
```asm
inc %eax
```
or
```asm
add $0x1, %eax    # a compiler may decide to use ADD instead of INC
```

Learn how to increment or decrement the contents in registers and memory cells.

Introduction to the Course

Memory, Registers, and Simple Arithmetic

Code Optimization

Number Representations

Pointers

Bytes, Words, Double, and Quad Words

Pointers to Memory

Logical Instructions and RIP

Reconstructing a Program with Pointers

Memory and Stacks

Frame Pointer and Local Variables

Function Parameters

More Instructions

Function Pointer Parameters

Summary of Code Disassembly Patterns

x64 Debugging, Disassembly & Reversing Exam

Incrementing and Decrementing Numbers

Increment and decrement numbers

Increment and decrement in C and C++

Increment and decrement in assembly language