> For the complete documentation index, see [llms.txt](https://alham-rizvi.gitbook.io/alhamrizvi/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://alham-rizvi.gitbook.io/alhamrizvi/picoctf-writeups/picoctf/reverse-engineering/gdb-test-drive.md).

# GDB test Drive

```bash
chmod +x gdbme
```

* Makes the file **executable**
* Without this, Linux won’t let you run `./gdbme`

***

#### 2.

```bash
gdb gdbme
```

* Opens the binary inside **GNU Debugger (GDB)**
* You can now inspect, pause, and manipulate execution

***

#### 3.

```gdb
layout asm
```

* Switches GDB to **assembly view (TUI mode)**
* Shows:
  * Disassembled instructions
  * Current instruction pointer (RIP)
* Useful for reverse engineering when no source code is available

***

#### 4.

```gdb
break *(main+99)
```

* Sets a **breakpoint at an exact memory offset**
* Meaning:
  * Go to function `main`
  * Move **99 bytes forward**
  * Stop execution there

👉 Why?

* You already analyzed the binary and found:
  * At `main+99` → some check happens (like password validation / failure branch)

***

#### 5.

```gdb
run
```

* Starts execution of the program
* It will **pause automatically** when it hits the breakpoint at `main+99`

***

#### 6.

```gdb
jump *(main+104)
```

* This is the **important trick**
* It **forces execution to jump to another instruction**
* Skips instructions between `+99` and `+104`

👉 In CTF context:

* You’re likely skipping:
  * a comparison (`cmp`)
  * a conditional jump (`jne`, `je`, etc.)
* So instead of:

  ```
  if (wrong) → exit
  ```

  you force:

  ```
  go directly to "correct" path
  ```


---

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