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

C4-L3

C4-L4

C4-L5

C6-L3

C8-L1

C9-L3

C10-L2

C10-L3

C11-L2

C13-L1

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

## Pointers revisited

The **pointer** is _a memory cell or a register that contains the address of another memory cell._ Memory pointers have their own addresses because they are memory cells too. In $32$-bit Linux, pointers are $32$-bit, and in $64$-bit Linux, pointers are $64$-bit.

## Addressing types

Memory cells can contain one byte, halfword, word, or doubleword. Therefore, a pointer can point to a byte, a halfword, a word, a doubleword, or a quadword. GDB disassembly output displays the suffix `l` in instructions involving pointers to $32$-bit (doubleword size) values.

Here are some illustrated examples:
```asm
movb $0xFF, (%rax)
```
The layout of memory before the `movb` instruction execution is shown in the figure below:

# Pointers revisited

The **pointer** is _a memory cell or a register that contains the address of another memory cell._ Memory pointers have their own addresses because they are memory cells too. In $32$-bit Linux, pointers are $32$-bit, and in $64$-bit Linux, pointers are $64$-bit.

# Addressing types

Memory cells can contain one byte, halfword, word, or doubleword. Therefore, a pointer can point to a byte, a halfword, a word, a doubleword, or a quadword. GDB disassembly output displays the suffix `l` in instructions involving pointers to $32$-bit (doubleword size) values.

Here are some illustrated examples:
```asm
movb $0xFF, (%rax)
```
The layout of memory before the `movb` instruction execution is shown in the figure below:

Learn how pointers are used to address memory cells and registers, as well as addressing different memory granularity in assembly language.

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

Declaring Pointers for Different Addressing Types

Pointers revisited

Addressing types