The Day I Reverse Engineered a Gameboy Advance Game (Revisited)

Gameboy Advance was one of the most popular video game platforms of its time and, because of it, many people worked together as a community to study and to document its architecture and develop ROM hacking and other interesting tools.

It turns out that this video game is a fantastic way to start studying reverse engineering: its architecture is very well documented and simpler if compared to the current game console generation – and, of course, it is very fun to work in a game-related project.

So... what do you think of learning reverse engineering through this challenge: developing a level editor for a GBA game called "Klonoa: Empire of Dreams"?
We need to understand the architecture behind ARM hardware, apply reverse engineering in order to discover how the logic of the game works, and then use our front-end knowledge (JS + React.js) to build a level editor.

Transcript

1. The day I reverse engineered a Gameboy Advance game With @ythecombinator AND @macabeus REVISITED
2. WTF?! THE DAY I REVERSE ENGINEERED A GAMEBOY ADVANCE GAME
3. """
5. soooo…
7. This is macabeus
8. This is MATHEUS
9. This is US PLAYING KLONOA
10. AND THIS IS US BORED
11. soooo…
12. WANTED MORE LEVELS TO PLAY WITH
13. WANTED DIFFERENT LEVELS
14. soooo…
15. soooo…
16. soooo…AND THIS IS KLONNOA
19. http://bit.ly/balccon-gba-code
20. Stretching the bridge THE DAY I REVERSE ENGINEERED A GAMEBOY ADVANCE GAME
21. https://www.nogba.com
22. https://www.hex-rays.com/products/ida
25. This is the tile ID. In this example, all tiles with the ID 9B are exactly the bridge part, which is the left corner. 9A is the ID of the continuous part of the bridge.
26. This tells us where the tile is stored in the memory. In this example, it is at 0600F1AD.
27. https://www.coranac.com/tonc/text/hardware.htm
28. https://www.coranac.com/tonc/text/hardware.htm The address found is expected 0600F1AD given that everything between 0600 and 0601 is part of the section known as VRAM.
29. Our bridge starts here!
30. And now we grow it bigger! WTF??!
31. Understanding the DMA THE DAY I REVERSE ENGINEERED A GAMEBOY ADVANCE GAME
32. VRAM pulls the tilemap
 containing exactly what the player has to see from somewhere else that has the entire thing.
33. https://www.coranac.com/tonc/text/regbg.htm
34. https://www.coranac.com/tonc/text/regbg.htm Direct Memory Access
35. https://www.coranac.com/tonc/text/regbg.htm It is a feature of computer systems that allows certain hardware subsystems to access main system memory (random- access memory), independent of the CPU
36. https://www.coranac.com/tonc/text/regbg.htm tldr; a faster copy and paste
37. DMA3: 03000900 0600E000 80000400 DMA3: 03001100 0600E800 80000400 DMA3: 03004DB0 0600F000 80000200 DMA3: 03004800 07000000 84000048
38. DMA3: 03000900 0600E000 80000400 DMA3: 03001100 0600E800 80000400 DMA3: 03004DB0 0600F000 80000200 DMA3: 03004800 07000000 84000048 The closest to the bytes of our bridge (0600F1AD).
39. DMA3: 03000900 0600E000 80000400 DMA3: 03001100 0600E800 80000400 DMA3: 03004DB0 0600F000 80000200 DMA3: 03004800 07000000 84000048 This address is the VRAM data source. It’s located in a region called Fast WRAM.
41. Our bridge starts here!
42. Stretching it… …It works! And…
43. Stretching it… …It works! And… WTF??!
44. Our extra tiles disappear when out of the player vision range.
45. LET’S TALK ABOUT PHYSICS THE DAY I REVERSE ENGINEERED A GAMEBOY ADVANCE GAME
46. Object Attribute Memory
47. OAM
49. This is the address in which Klonoa is stored on the memory
50. DMA3: 03000900 0600E000 80000400 DMA3: 03001100 0600E800 80000400 DMA3: 03004DB0 0600F000 80000200 DMA3: 03004800 07000000 8400003E
51. DMA3: 03000900 0600E000 80000400 DMA3: 03001100 0600E800 80000400 DMA3: 03004DB0 0600F000 80000200 DMA3: 03004800 07000000 8400003E We can see exactly the byte that writes on Klonoa’s object (03004800).
52. DMA3: 03000900 0600E000 80000400 DMA3: 03001100 0600E800 80000400 DMA3: 03004DB0 0600F000 80000200 DMA3: 03004800 07000000 8400003E We can see exactly the byte that writes on Klonoa’s OAM (03004800).
56. 1 2
62. Here is where Y fixes Klonoa’s position Here is where which decides if should fix or not Klonoa’s position
64. https://www.coranac.com/tonc/text/hardware.htm
65. https://www.coranac.com/tonc/text/hardware.htm
67. Let’s find the tilemap on rom THE DAY I REVERSE ENGINEERED A GAMEBOY ADVANCE GAME
68. Cartridge Fast WRAM Display Slow WRAM VRAM > > > > The data flow
69. Cartridge Fast WRAM Display VRAM Slow WRAM > > > > Our research flow
70. swi 11h what?
71. Swi
72. SoftWare Interrupt
73. SoftWare Interrupt = Bios calls
74. BIOS is a firmware that is intended to initialise the physical components of the system In GBA, its BIOS exposes many functions often used in games, including data compression and decompression Each function has an associated numeric code, which must be used as a parameter in the SWI statement
75. Input: How division works on ARM Assembly swi 0x06 R0
 numerator R1
 denominator R0
 numerator / denominator R1
 numerator % denominator R3
 abs(numerator / denominator) Output:
77. Huffman + lz77 = deflate
82. 6E 6E 6E B0 B1 BD 77 AB B3 AB B3 7C 6E 6E 6E 6E 6E 6E 6E 6E 7C 6E 6E 6E 6E 7C 6E 6E
83. 6E 6E 6E B0 B1 BD 77 AB B3 AB B3 7C 6E 6E 6E 6E 6E 6E 6E 6E 7C 6E 6E 6E 6E 7C 6E 6E 6E 6E 6E B0 B1 BD 77 AB B3 AB B3 7C 6E 6E 6E 6E 6E 6E 6E 6E 7C 6E 6E 6E 6E 7C 6E 6E
84. 6E 6E 6E B0 B1 BD 77 AB B3 AB B3 7C 6E 6E 6E 6E 6E 6E 6E 6E 7C 6E 6E 6E 6E 7C 6E 6E 6E 6E 6E B0 B1 BD 77 AB B3 AB B3 7C 6E 6E 6E 6E 6E 6E 6E 6E 7C 6E 6E 6E 6E 7C 6E 6E =
85. Let’s paint the tilemap THE DAY I REVERSE ENGINEERED A GAMEBOY ADVANCE GAME
86. 0x1A 0x1B 0x1C 0x1D 0x1E 0x1F
87. 0x1A 0x1B 0x1C 0x1D 0x1E 0x1F 0x1A 0x1B 0x1C 0x1D 0x1E 0x1F 0x1A 0x1B 0x1C 0x1D 0x1E 0x1F 0x1A 0x1B 0x1C 0x1D 0x1E 0x1F
88. H · W = 25023
 H,W ∈ ℕ
89. x x x x a x x x x x x x x b x x x x I’m on tile a
90. x x x x a x x x x x x x x b x x x x I’m on tile a x x x x a x x x x x x x x b x x x x From the tile a to b there are 9 bytes (= 9 tiles), so the length of the tilemap is exactly 9
92. Breakpoint here
93. …is located here This byte…
95. As I change this byte…
96. …it reflects right here
98. Changing these bytes…
99. …we drop Klonoa one level below
101. Changing these bytes… …we found the B tile!
102. 020085DB The length of the level is 420! - 02008437 = 1A4 (420)
103. https://github.com/oliver-moran/jimp
104. const Jimp = require('jimp') const { drop } = require('ramda') const fs = require('fs') const data = drop(3, fs.readFileSync('dump/level-2/tilemap'))
105. const getPixelColor = hexTile "# { if (hexTile === 0) { return 0x00000000 } return 0xFFFFFFFF }
106. new Jimp(300, 600, (err, image) "# { let x = 0 let y = 0 for (let i = 0; i < data.length; i += 1) { const value = data[i] x += 1 if (x === 300) { y += 1 x = 0 } let color = getPixelColor(value) image.setPixelColor(color, x, y) } image.write('image.png') })
112. Let’s find and paint the objects THE DAY I REVERSE ENGINEERED A GAMEBOY ADVANCE GAME
115. DMA3: 03000900 0600E000 80000400 DMA3: 03001100 0600E800 80000400 DMA3: 03004DB0 0600F000 80000200 DMA3: 03004800 07000000 8400003E Update the OAM
116. DMA3: 03000900 0600E000 80000400 DMA3: 03001100 0600E800 80000400 DMA3: 03004DB0 0600F000 80000200 DMA3: 03004800 07000000 8400003E Update the OAM
117. DMA3: 03000900 0600E000 80000400 DMA3: 03001100 0600E800 80000400 DMA3: 03004DB0 0600F000 80000200 DMA3: 03004800 07000000 8400003E Update the OAM 0300480A:0300480B ✘
118. C
122. Global OAM
123. > > > > 08051440 08003CD4 0800B602 0800B634 0804505C
125. ROM OAM
128. Global OAM OAM > ROM OAM >
130. ROM OAM of the first level 08367700 083686B0 08369380 ROM OAM of the third level ROM OAM of the second level Hole Hole . . .
131. const [ xFirstPosition, yFirstPosition, xSecondPosition, ySecondPosition, xThirdPosition, yThirdPosition, xFourthPosition, yFourthPosition, xFifthPosition, yFifthPosition, kind, ] = qunpack.unpack('v2 x4 v2 x4 v2 x4 v2 x4 v2 x5 c', bytes);
132. const [ xFirstPosition, yFirstPosition, xSecondPosition, ySecondPosition, xThirdPosition, yThirdPosition, xFourthPosition, yFourthPosition, xFifthPosition, yFifthPosition, kind, ] = qunpack.unpack('v2 x4 v2 x4 v2 x4 v2 x4 v2 x5 c', bytes); ✘
133. const { xStage1, yStage1, xStage2, yStage2, xStage3, yStage3, xStage4, yStage4, xStage5, yStage5, kind, } = binary.parse(memory) .word16lu('xStage1').word16lu('yStage1') .skip(4) .word16lu('xStage2').word16lu('yStage2') .skip(4) .word16lu('xStage3').word16lu('yStage3') .skip(4) .word16lu('xStage4').word16lu('yStage4') .skip(4) .word16lu('xStage5').word16lu('yStage5') .skip(5) .word8lu('kind') .vars
135. let’s see the project THE DAY I REVERSE ENGINEERED A GAMEBOY ADVANCE GAME
136. Coding THE DAY I REVERSE ENGINEERED A GAMEBOY ADVANCE GAME
137. soooo…
138. Stack
139. React.js
140. Webpack
141. Ramda.js
142. architecture
143. ✂ Brush Scissors
144. klo-gba.js/scissors/src/visions/
145. export default { rom: { tilemap: [0x1B27FC, 0x1B36F3], oam: [0xE2B90, 0xE2F59], portals: [0xD48C8, 0xD48EF], }, tilemap: { totalStages: 3, height: 60, width: 420, scheme: [ { name: 'grass', ids: [0x7D, 0x80, 0x81, 0x82, 0x8E, 0x8F, 0x90], },
146. export default { rom: { tilemap: [0x1B27FC, 0x1B36F3], oam: [0xE2B90, 0xE2F59], portals: [0xD48C8, 0xD48EF], }, tilemap: { totalStages: 3, height: 60, width: 420, scheme: [ { name: 'grass', ids: [0x7D, 0x80, 0x81, 0x82, 0x8E, 0x8F, 0x90], },
147. export default { rom: { tilemap: [0x1B27FC, 0x1B36F3], oam: [0xE2B90, 0xE2F59], portals: [0xD48C8, 0xD48EF], }, tilemap: { totalStages: 3, height: 60, width: 420, scheme: [ { name: 'grass', ids: [0x7D, 0x80, 0x81, 0x82, 0x8E, 0x8F, 0x90], },
148. { name: 'rock', ids: [0x54, 0x53, 0x55, 0x56, 0x57, 0x58, 0x59, }, { name: 'darkRock', ids: [0x40, 0x41, 0x42, 0x43, 0x44, 0x45, 0x46, }, { name: 'wood', ids: [0x52, 0x94, 0x98, 0x99, 0x9A, 0x9B, 0x9D, }, { name: 'bridgeRope', ids: [0x04, 0x05, 0x0B, 0x0C, 0x11, 0x13, 0x14,
149. { name: 'spike', ids: [0x3D], }, ], },
150. Web assembly
151. Tilemap compressed Old C code to uncompress it Decompressed Tilemap > >
152. Tilemap compressed Old C code to uncompress it Decompressed Tilemap > > Can’t run C code on browser!
153. Tilemap compressed Old C code to uncompress it Decompressed Tilemap > >
154. Tilemap compressed Old C code to uncompress it Decompressed Tilemap > > >Emscripten >WebAssembly
155. huffman.c lzss.c > > Emscripten huffman.js lzss.js huffman.wasm lzss.wasm +
156. class HuffmanDecodeError extends Error { constructor (e) { super(`Error when tried to use huffman decoder: ${e}`) this.name = 'HuffmanDecodeError' } } huffmanModule.onRuntimeInitialized = () "# {} const huffmanDecode = (buffer) "# { FS.writeFile('file', buffer)
157. class HuffmanDecodeError extends Error { constructor (e) { super(`Error when tried to use huffman decoder: ${e}`) this.name = 'HuffmanDecodeError' } } huffmanModule.onRuntimeInitialized = () "# {} const huffmanDecode = (buffer) "# { FS.writeFile('file', buffer)
158. const huffmanDecode = (buffer) "# { FS.writeFile('file', buffer) huffmanModule._HUF_Decode() try { return huffmanModule.FS.readFile('file', { encoding: 'binary' }) } catch (e) { throw new HuffmanDecodeError(e) } }
159. function docker_run_emscripten { local filename="$1" echo "Compiling $filename$$." docker run \ --rm -it \ -v $(pwd)/scissors/src/wasm:/src \ trzeci/emscripten \ emcc -s WASM=1 -s ALLOW_MEMORY_GROWTH=1 -s MODULARIZE=1 -s EXTRA_EXPORTED_RUNTIME_METHODS=[\"FS\"] -s EXPORT_NAME=\"$filename\" -o ./$filename.js $filename.c } docker_run_emscripten huffman docker_run_emscripten lzss
160. function docker_run_emscripten { local filename="$1" echo "Compiling $filename$$." docker run \ --rm -it \ -v $(pwd)/scissors/src/wasm:/src \ trzeci/emscripten \ emcc -s WASM=1 -s ALLOW_MEMORY_GROWTH=1 -s MODULARIZE=1 -s EXTRA_EXPORTED_RUNTIME_METHODS=[\"FS\"] -s EXPORT_NAME=\"$filename\" -o ./$filename.js $filename.c } docker_run_emscripten huffman docker_run_emscripten lzss
161. const extractFullTilemap = (romBuffer, [addressStart, addressEnd]) "# romBuffer.slice(addressStart, addressEnd) |> huffmanDecode |> lzssDecode
162. Tilemap
164. ✔ Display tiles and OAM ✔ Allow the user to edit it
165. https://github.com/konvajs/konva
167. 1st load: ˜3 seconds! 2nd load: ˜13 seconds!
168. After some React.js performance work…
169. 1st load
170. 1st load ˜1.8 seconds!
171. 1st load 2nd load
172. 1st load 2nd load ˜3.6 seconds!
173. After switching from Canvas to WebGL…
174. 1st load
175. 1st load ˜1.6 seconds!
176. 1st load ˜1.6 seconds! 2nd load
177. 1st load ˜1.6 seconds! 2nd load ˜2.8 seconds!
178. After doing more optimizations on WebGL…
179. 1st load
180. 1st load ˜625 ms!
181. 1st load 2nd load ˜625 ms!
182. 1st load 2nd load ˜536 ms! ˜625 ms!
183. 1st load: ˜3 seconds! 2nd load: ˜13 seconds! Perf recap: No one is gonna play with this
184. 1st load: ˜3 1.8 seconds! 2nd load: ˜13 3.6 seconds! Perf recap: Removing wasted renders and other React optimisation stuff.
185. 1st load: ˜3 1.8 1.6 seconds! 2nd load: ˜13 3.6 2.8 seconds! Perf recap: Canvas → WebGL
186. 1st load: ˜3 1.8 1.6 0.625 seconds! 2nd load: ˜13 3.6 2.8 0.536 seconds! Perf recap: React → WebGL
187. Saving the new tilemap
188. Each level is stored continually in the memory First Level Second Level Third Level
189. First Level Second Level Third Level > Changes in the first level
190. First Level Second Level Third Level > Customised First Level > Changes in the first level
191. Second Level Third Level First Level Second Level Third Level > Customised First Level > Changes in the first level
192. Second Level Third Level First Level Second Level Third Level > Customised First Level > Changes in the first level
194. ARM Thumb Faster to execute Instructions demands less memory Can perform instructions more complex
195. The switch between ARM and Thumb must be done by bx instruction. And this instruction only can read a register
196. Instructions to load a level . . . . . . . . . Very big hole space at the end of cartridge First Level__ Second Level__ Third Level__ 081B27FC 081B3E5C 081B50AC Instructions to load a level
197. First Level__ Second Level__ Third Level__ . . . . . . . . . 081B27FC 081B3E5C 081B50AC Instructions to load a level Customised First Level__ Customised level loader Constant addresses map table Hole Customised Second Level__ Hole Customised Third Level__ Hole Hole 08367700 083686B0 08369380
198. Instructions to load a level 08367620 FC 27 1B 08 08367624 00 77 36 08 08367628 5C 3E 1B 08 0836762C B0 86 36 08 08367620 AC 50 1B 08 08367634 80 93 36 08 First Level__ Second Level__ Third Level__ . . . . . . . . . 081B27FC 081B3E5C 081B50AC Customised First Level__ Customised level loader Constant addresses map table Hole Customised Second Level__ Hole Customised Third Level__ Hole Hole 08367700 083686B0 08369380
199. Instructions to load a level 08367620 FC 27 1B 08 08367624 00 77 36 08 08367628 5C 3E 1B 08 0836762C B0 86 36 08 08367620 AC 50 1B 08 08367634 80 93 36 08 First Level__ Second Level__ Third Level__ . . . . . . . . . 081B27FC 081B3E5C 081B50AC Customised First Level__ Customised level loader Constant addresses map table Hole Customised Second Level__ Hole Customised Third Level__ Hole Hole 08367700 083686B0 08369380
200. Instructions to load a level 08367620 FC 27 1B 08 08367624 00 77 36 08 08367628 5C 3E 1B 08 0836762C B0 86 36 08 08367620 AC 50 1B 08 08367634 80 93 36 08 First Level__ Second Level__ Third Level__ . . . . . . . . . 081B27FC 081B3E5C 081B50AC Customised First Level__ Customised level loader Constant addresses map table Hole Customised Second Level__ Hole Customised Third Level__ Hole Hole 08367700 083686B0 08369380
201. Instructions to load a level 08367620 FC 27 1B 08 08367624 00 77 36 08 08367628 5C 3E 1B 08 0836762C B0 86 36 08 08367620 AC 50 1B 08 08367634 80 93 36 08 First Level__ Second Level__ Third Level__ . . . . . . . . . 081B27FC 081B3E5C 081B50AC Customised First Level__ Customised level loader Constant addresses map table Hole Customised Second Level__ Hole Customised Third Level__ Hole Hole 08367700 083686B0 08369380
202. Instructions to load a level (patched) First Level__ Second Level__ Third Level__ . . . . . . . . . 081B27FC 081B3E5C 081B50AC Customised First Level__ Customised level loader Constant addresses map table Hole Customised Second Level__ Hole Customised Third Level__ Hole Hole 08367700 083686B0 08369380 Original loader Patched loader 08043B0A mov r4,r0 08043B0C bl 08367610h 08043B10 bl 0805143Ch 08043B0A mov r4,r0 08043B0C add r0,r5,4 08043B0E mov r1,r4 08043B10 bl 0805143Ch
203. Instructions to load a level (patched) First Level__ Second Level__ Third Level__ . . . . . . . . . 081B27FC 081B3E5C 081B50AC Customised First Level__ Customised level loader Constant addresses map table Hole Customised Second Level__ Hole Customised Third Level__ Hole Hole 08367700 083686B0 08369380 R0 is the pointer to where is the tilemap that will load Original loader Patched loader 08043B0A mov r4,r0 08043B0C bl 08367610h 08043B10 bl 0805143Ch 08043B0A mov r4,r0 08043B0C add r0,r5,4 08043B0E mov r1,r4 08043B10 bl 0805143Ch
204. Instructions to load a level (patched) First Level__ Second Level__ Third Level__ . . . . . . . . . 081B27FC 081B3E5C 081B50AC Customised First Level__ Customised level loader Constant addresses map table Hole Customised Second Level__ Hole Customised Third Level__ Hole Hole 08367700 083686B0 08369380 Original loader Patched loader 08043B0A mov r4,r0 08043B0C bl 08367610h 08043B10 bl 0805143Ch 08043B0A mov r4,r0 08043B0C add r0,r5,4 08043B0E mov r1,r4 08043B10 bl 0805143Ch
205. Instructions to load a level (patched) First Level__ Second Level__ Third Level__ . . . . . . . . . 081B27FC 081B3E5C 081B50AC Customised First Level__ Customised level loader Constant addresses map table Hole Customised Second Level__ Hole Customised Third Level__ Hole Hole 08367700 083686B0 08369380 08367610 mov r0,r15 08367612 add r0,3Ch 08367614 bx r0
206. Instructions to load a level (patched) First Level__ Second Level__ Third Level__ . . . . . . . . . 081B27FC 081B3E5C 081B50AC Customised First Level__ Customised level loader Constant addresses map table Hole Customised Second Level__ Hole Customised Third Level__ Hole Hole 08367700 083686B0 08369380 08367650 add r0,r4,4h 08367654 ldr r4,[r15,#-3Ch] 08367658 cmp r0,r4 0836765C ldreq r0,[r15,#-40h] 08367654 ldr r4,[r15,#-40h] 08367658 cmp r0,r4 0836765C ldreq r0,[r15,#-44h] 08367654 ldr r4,[r15,#-44h] 08367658 cmp r0,r4 0836765C ldreq r0,[r15,#-48h] 08367660 mov r4,r1 08367664 bx r14
207. Instructions to load a level (patched) First Level__ Second Level__ Third Level__ . . . . . . . . . 081B27FC 081B3E5C 081B50AC Customised First Level__ Customised level loader Constant addresses map table Hole Customised Second Level__ Hole Customised Third Level__ Hole Hole 08367700 083686B0 08369380 08367650 add r0,r4,4h 08367654 ldr r4,[r15,#-3Ch] 08367658 cmp r0,r4 0836765C ldreq r0,[r15,#-40h] 08367654 ldr r4,[r15,#-40h] 08367658 cmp r0,r4 0836765C ldreq r0,[r15,#-44h] 08367654 ldr r4,[r15,#-44h] 08367658 cmp r0,r4 0836765C ldreq r0,[r15,#-48h] 08367660 mov r4,r1 08367664 bx r14
208. Instructions to load a level (patched) First Level__ Second Level__ Third Level__ . . . . . . . . . 081B27FC 081B3E5C 081B50AC Customised First Level__ Customised level loader Constant addresses map table Hole Customised Second Level__ Hole Customised Third Level__ Hole Hole 08367700 083686B0 08369380 08367650 add r0,r4,4h 08367654 ldr r4,[r15,#-3Ch] 08367658 cmp r0,r4 0836765C ldreq r0,[r15,#-40h] 08367654 ldr r4,[r15,#-40h] 08367658 cmp r0,r4 0836765C ldreq r0,[r15,#-44h] 08367654 ldr r4,[r15,#-44h] 08367658 cmp r0,r4 0836765C ldreq r0,[r15,#-48h] 08367660 mov r4,r1 08367664 bx r14
209. Instructions to load a level (patched) First Level__ Second Level__ Third Level__ . . . . . . . . . 081B27FC 081B3E5C 081B50AC Customised First Level__ Customised level loader Constant addresses map table Hole Customised Second Level__ Hole Customised Third Level__ Hole Hole 08367700 083686B0 08369380 08367650 add r0,r4,4h 08367654 ldr r4,[r15,#-3Ch] 08367658 cmp r0,r4 0836765C ldreq r0,[r15,#-40h] 08367654 ldr r4,[r15,#-40h] 08367658 cmp r0,r4 0836765C ldreq r0,[r15,#-44h] 08367654 ldr r4,[r15,#-44h] 08367658 cmp r0,r4 0836765C ldreq r0,[r15,#-48h] 08367660 mov r4,r1 08367664 bx r14
210. Instructions to load a level (patched) First Level__ Second Level__ Third Level__ . . . . . . . . . 081B27FC 081B3E5C 081B50AC Customised First Level__ Customised level loader Constant addresses map table Hole Customised Second Level__ Hole Customised Third Level__ Hole Hole 08367700 083686B0 08369380 08367650 add r0,r4,4h 08367654 ldr r4,[r15,#-3Ch] 08367658 cmp r0,r4 0836765C ldreq r0,[r15,#-40h] 08367654 ldr r4,[r15,#-40h] 08367658 cmp r0,r4 0836765C ldreq r0,[r15,#-44h] 08367654 ldr r4,[r15,#-44h] 08367658 cmp r0,r4 0836765C ldreq r0,[r15,#-48h] 08367660 mov r4,r1 08367664 bx r14
211. 1. Redirect to the patched code 2. Check if the R0 is on the table 3. If yes, load the associated value 4. Return to the original loader
216. Result THE DAY I REVERSE ENGINEERED A GAMEBOY ADVANCE GAME
222. THE Future THE DAY I REVERSE ENGINEERED A GAMEBOY ADVANCE GAME
225. WE ARE... THE DAY I REVERSE ENGINEERED A GAMEBOY ADVANCE GAME
226. MACABEUS macabeus ____ www.macalogs.com.br _ _ Software Engineer, full-stack @CASAFARI Always creating crazy projects
227. MATHEUS ALBUQUERQUE YTHECOMBINATOR www.ythecombinator.space LAND@YTHECOMBINATOR.SPACE Software Engineer, Front- End @STRV addicted to emojis, memes and beer
228. Benjamin Stauffer kcowolf TRANSLATOR
229. Raul peres behance.net/Kniksis illustrator
230. This talk THE DAY I REVERSE ENGINEERED A GAMEBOY ADVANCE GAME
231. http://bit.ly/balccon-gba-keynote
232. http://bit.ly/balccon-gba-code
233. http://bit.ly/balccon-gba-posts
235. We got stickers!
236. Hvala THANKS @ythecombinator AND @macabeus