# Embedded Systems Reverse Engineering
[Repository](https://github.com/mytechnotalent/Embedded-Hacking)

## Week 2
Hello, World - Debugging and Hacking Basics: Debugging and Hacking a Basic Program for the Pico 2

### Exercise 4: Automate the Hack

#### Objective
Create a reusable GDB command that injects a string into SRAM, repoints `r0`, and resumes execution with a single call.

#### Prerequisites
- Pico 2 connected with OpenOCD, GDB, and serial monitor ready
- `build/0x0001_hello-world.elf` available
- Familiarity with breaking at `0x1000023c` and injecting strings from prior exercises

#### Task Description
You will define a custom GDB command `hack` that writes a payload to `0x20000000`, repoints `r0`, and continues execution automatically.

#### Step-by-Step Instructions

##### Step 1: Connect, Halt, and Break

```gdb
(gdb) target extended-remote :3333
(gdb) monitor reset halt
(gdb) b *0x1000023c
(gdb) c
```

##### Step 2: Define the `hack` Command

```gdb
(gdb) define hack
> set {char[14]} 0x20000000 = {'h','a','c','k','y',',',' ','w','o','r','l','d','\r','\0'}
> set $r0 = 0x20000000
> c
> end
```

##### Step 3: Invoke the Command

```gdb
(gdb) hack
```

##### Step 4: Observe Output
- PuTTY should immediately show your injected string after the command runs.
- The breakpoint will be re-hit on the next loop iteration; rerun `hack` if you want to reapply after changes.

#### Expected Output
- `hack` executes without errors, writes the payload, updates `r0`, and resumes execution.
- Serial output reflects the injected message.

#### Questions for Reflection

###### Question 1: How could you parameterize the command to accept different strings or addresses?

###### Question 2: What happens if you define `hack` before setting the breakpoint—will it still work as expected?

###### Question 3: How would you adapt this pattern for multi-step routines (e.g., patch, dump, continue)?

#### Tips and Hints
- Redefine `hack` any time you want a different payload; GDB will overwrite the prior definition.
- Keep the payload length aligned with the buffer size to avoid stray bytes.
- If the target keeps running past the breakpoint, ensure hardware breakpoints are available and set correctly.

#### Next Steps
- Create additional helper commands (e.g., `dumpstr`, `retarget`) to streamline experiments.
- Explore GDB scripting files (`.gdbinit`) to auto-load your helpers on startup.
- Try combining `hack` with watchpoints to observe memory changes live.
