Reverse Engineering & Binary Analysis Basics · Lesson

Memory and Register Examination

Practice inspecting memory regions, viewing register values, and modifying program state during execution.

Memory and Register Examination is a free Reverse Engineering & Binary Analysis Basics lesson on CoddyKit — lesson 3 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Reverse Engineering & Binary Analysis Basics learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.

Debugging's Core: Memory & Registers

When analyzing programs, especially during dynamic analysis, understanding what's happening inside the CPU is key. This means looking at registers and memory.

These are the CPU's direct workspaces, holding data and instructions that are actively being processed.

CPU's Scratchpad: Registers

Registers are tiny, super-fast storage locations directly within the CPU itself. Think of them as the CPU's "scratchpad" where it keeps data it needs immediately.

They hold temporary values, addresses, and control information.
Accessing data in registers is much faster than accessing RAM.
Different architectures (like x86, ARM) have different sets of registers.

Common x86/x64 Registers

While there are many registers, some are crucial for reverse engineering:

General-Purpose: RAX/EAX, RBX/EBX, RCX/ECX, RDX/EDX (used for data, function arguments, return values).
Stack Pointer: RSP/ESP (points to the top of the stack).
Base Pointer: RBP/EBP (points to the base of the current stack frame).
Instruction Pointer: RIP/EIP (points to the next instruction to execute).

Viewing Registers in GDB

Let's see how to inspect registers using a debugger like GDB. We'll use a simple C program.

First, compile with debug info (-g): gcc -g -o myprog myprog.c

After compiling and starting GDB (e.g., gdb -q ./myprog), you can set a breakpoint (break main), run (run), and then use info registers.

    #include <stdio.h>

    int main() {
        int a = 10;
        int b = 20;
        int sum = a + b;
        printf("Sum: %d\n", sum);
        return 0;
    }

Program's Workspace: Memory

Memory (RAM) is where your program stores larger amounts of data that aren't actively being processed by the CPU. This includes variables, program code, and other resources.

Every byte in memory has a unique address. When a program runs, it gets its own dedicated "virtual" memory space.

Simplified Memory Layout

A program's memory is typically divided into sections:

Text/Code Segment: Contains the executable instructions.
Data Segment: Stores global and static variables.
Heap: Used for dynamically allocated memory (e.g., with malloc).
Stack: Used for local variables, function arguments, and return addresses.

Viewing Memory in GDB

To inspect memory in GDB, we use the x command (examine memory). It has a flexible syntax:

x /NFS ADDRESS
N: Number of units to display (optional).
F: Format (e.g., x for hex, d for decimal, s for string, i for instruction).
S: Size (e.g., b for byte, h for halfword (2 bytes), w for word (4 bytes), g for giant (8 bytes)).

Example: Viewing a Stack Variable

Let's use our previous program. Compile it and set a breakpoint before printf. Then, we can find the address of sum and examine its content.

Run this code, then attach GDB (gdb -q ./myprog), set a breakpoint at line 7 (break main.c:7), and run (run).

In GDB: p &sum to get its address. Finally, x /w ADDRESS_OF_SUM to view its 4-byte value.

    #include <stdio.h>

    int main() {
        int a = 10;
        int b = 20;
        int sum = a + b; // Breakpoint here
        printf("Sum: %d\n", sum);
        return 0;
    }

Changing Register Values

A powerful debugging technique is to modify register values on the fly. This can change how a program behaves without altering its code.

In GDB, you can use the set command:

set $rax = 0x1234
set $rip = *0x400500 (jump to a new address)

This is useful for bypassing checks or redirecting execution flow.

Altering Memory Content

Just like registers, you can also modify memory content while debugging. This allows you to change variable values, strings, or even instructions in memory.

Using GDB's set command:

set var_name = new_value (if the variable is in scope)
set {int}0x400000 = 123 (change 4 bytes at address 0x400000 to 123)

Be careful, incorrect modifications can crash the program!

Debugger Challenge

You're debugging a program. You want to see the value of a 4-byte integer variable named counter located at memory address 0x7fffffff0000. What GDB command would you use?

Recap: Debugging's Core

Today, we explored how to examine and modify the core components of a running program: registers and memory.

Registers are CPU's fast storage, viewed with info registers.
Memory holds larger data, viewed with x /NFS ADDRESS.
Both can be modified with set to alter program state dynamically.

These skills are fundamental for understanding program execution and reverse engineering!

Frequently asked questions

Is the “Memory and Register Examination” lesson free?

Yes — the full text of “Memory and Register Examination” is free to read here on the web, and the Reverse Engineering & Binary Analysis Basics course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Reverse Engineering & Binary Analysis Basics course, upgrade to CoddyKit PRO.

What will I learn in “Memory and Register Examination”?

Practice inspecting memory regions, viewing register values, and modifying program state during execution. You practise Reverse Engineering & Binary Analysis Basics with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start Reverse Engineering & Binary Analysis Basics?

No prior experience is required. Reverse Engineering & Binary Analysis Basics on CoddyKit is structured for beginners through advanced learners; this is — lesson 3 of 4, so you can start here or from the beginning and move at your own pace.

How long does the “Memory and Register Examination” lesson take?

Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.

Can I write and run code in this Reverse Engineering & Binary Analysis Basics lesson?

Yes. Every Reverse Engineering & Binary Analysis Basics lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.

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