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WEEK02/WEEK02-04.md

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+# 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.