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Fix Week 7 ASCII-art arrow mojibake and regenerate PDF

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Kevin Thomas committed 2026-10-01 11:46:31 -04:00
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commit 62e8a2ca70
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+16 -16
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WEEK07/WEEK07.md
+16 -16
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@@ -62,7 +62,7 @@ Think of it like a "find and replace" in a text editor. The compiler never sees
| Source Code Preprocessor Compiler |
| +----------+ +----------+ +----------+ |
| | #define | | Replace | | Compile | |
| | FAV_NUM | -----? | FAV_NUM | -----? | binary | |
| | FAV_NUM | -----> | FAV_NUM | -----> | binary | |
| | 42 | | with 42 | | code | |
| +----------+ +----------+ +----------+ |
| |
@@ -175,7 +175,7 @@ Every I2C device has a unique **7-bit address**. Common addresses:
| 5. Receiver sends ACK after each byte |
| 6. Master sends STOP condition |
| |
| START --? Address --? ACK --? Data --? ACK --? STOP |
| START --> Address --> ACK --> Data --> ACK --> STOP |
| |
+-----------------------------------------------------------------+
```
@@ -269,16 +269,16 @@ When you write `I2C_PORT` in your code, here's what happens:
| |
| In your code: #define I2C_PORT i2c1 |
| | |
| ? |
| ↓ |
| In i2c.h: #define i2c1 (&i2c1_inst) |
| | |
| ? |
| ↓ |
| In i2c.c: i2c_inst_t i2c1_inst = {i2c1_hw, false}; |
| | |
| ? |
| ↓ |
| In i2c.h: #define i2c1_hw ((i2c_hw_t *)I2C1_BASE) |
| | |
| ? |
| ↓ |
| In addressmap.h: #define I2C1_BASE 0x40098000 |
| |
+-----------------------------------------------------------------+
@@ -373,15 +373,15 @@ Connect your LCD like this:
| Pico 2 1602 LCD + I2C Backpack |
| +----------+ +----------------------+ |
| | | | | |
| | GPIO 2 |------- SDA -----?| SDA | |
| | GPIO 2 |------- SDA ----->| SDA | |
| | (SDA) | | | |
| | | | +------------+ | |
| | GPIO 3 |------- SCL -----?| SCL| Reverse | | |
| | GPIO 3 |------- SCL ----->| SCL| Reverse | | |
| | (SCL) | | |Engineering | | |
| | | | +------------+ | |
| | 3.3V |------- VCC -----?| VCC | |
| | 3.3V |------- VCC ----->| VCC | |
| | | | | |
| | GND |------- GND -----?| GND | |
| | GND |------- GND ----->| GND | |
| | | | | |
| +----------+ +----------------------+ |
| |
@@ -484,7 +484,7 @@ OTHER_FAV_NUM: 1337
## Part 8: Debugging with GDB (Dynamic Analysis)
> ? **REVIEW:** This setup is identical to previous weeks. If you need a refresher on OpenOCD and GDB connection, refer back to Week 3 Part 6.
> **REVIEW:** This setup is identical to previous weeks. If you need a refresher on OpenOCD and GDB connection, refer back to Week 3 Part 6.
### Starting the Debug Session
@@ -819,7 +819,7 @@ movs r1, #0x2a -> bytes: 2a 21
In HxD, use **Ctrl+G** to navigate to file offset `28E` and verify you see the byte `2A` followed by `21`.
> ?? **How Thumb encoding works:** In `movs r1, #imm8`, the immediate value is the first byte, and the opcode `21` is the second byte. So the bytes `2a 21` encode `movs r1, #0x2a` (42). If you wanted to change this to 43, you'd change `2A` to `2B`.
> **How Thumb encoding works:** In `movs r1, #imm8`, the immediate value is the first byte, and the opcode `21` is the second byte. So the bytes `2a 21` encode `movs r1, #0x2a` (42). If you wanted to change this to 43, you'd change `2A` to `2B`.
### Step 18: Understand OTHER_FAV_NUM Encoding (movw - 32-bit Thumb-2)
@@ -836,9 +836,9 @@ This is the 32-bit Thumb-2 encoding of `movw r1, #0x539` (1337). The bytes break
+-----------------------------------------------------------------+
| movw r1, #0x539 -> bytes: 40 F2 39 51 |
| |
| Byte 0: 0x40 -?? |
| Byte 0: 0x40 -+ |
| Byte 1: 0xF2 -+ First halfword (opcode + upper imm bits) |
| Byte 2: 0x39 ---- Lower 8 bits of immediate (imm8) ?? CHANGE |
| Byte 2: 0x39 ---- Lower 8 bits of immediate (imm8) <- CHANGE |
| Byte 3: 0x51 ---- Destination register (r1) + upper imm bits |
| |
| imm16 = 0x0539 = 1337 decimal |
@@ -856,7 +856,7 @@ To change `movw r1, #1337` to `movw r1, #1344`:
3. You should see the byte `39` at this position
4. Change `39` to `40`
> ?? **Why offset `0x298` and not `0x296`?** The lower 8 bits of the immediate (`imm8`) are in the **third byte** of the 4-byte `movw` instruction. The instruction starts at file offset `0x296`, so imm8 is at `0x296 + 2 = 0x298`. Changing `0x39` to `0x40` changes the value from `0x539` (1337) to `0x540` (1344).
> **Why offset `0x298` and not `0x296`?** The lower 8 bits of the immediate (`imm8`) are in the **third byte** of the 4-byte `movw` instruction. The instruction starts at file offset `0x296`, so imm8 is at `0x296 + 2 = 0x298`. Changing `0x39` to `0x40` changes the value from `0x539` (1337) to `0x540` (1344).
### Step 19: Hack - Change LCD Text from "Reverse" to "Exploit"
@@ -1094,4 +1094,4 @@ The numbers are unchanged - we only patched the LCD string!
**Remember:** When you see complex nested structures in a binary, take your time to understand the hierarchy. Use GDB to examine struct layouts in memory and trace pointer chains. And always remember - even "constants" can be hacked!
Happy hacking! ?
Happy hacking!
WEEK07/WEEK07.pdf
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