M CHANGES → CHANGES

@@ -46,6 +46,7 @@ - SDL: Fix boundary conditions for joystick adjustments
  - Util: Fix a null-pointer issue when attempting to delete a key
  - SDL: Allocate properly sized input maps
  - ARM7: Handle writeback for PC in addressing modes 2 and 3
+ - GBA: Handle out-of-bounds I/O access
 Misc:
  - Qt: Show multiplayer numbers in window title
  - Qt: Handle saving input settings better

M src/gba/io.c → src/gba/io.c

@@ -489,6 +489,10 @@ // Some bad interrupt libraries will write to this
 			break;
 		default:
 			GBALog(gba, GBA_LOG_STUB, "Stub I/O register write: %03x", address);
+			if (address >= REG_MAX) {
+				GBALog(gba, GBA_LOG_GAME_ERROR, "Write to unused I/O register: %03X", address);
+				return;
+			}
 			break;
 		}
 	}
@@ -643,6 +647,10 @@ // Some bad interrupt libraries will read from this
 		break;
 	default:
 		GBALog(gba, GBA_LOG_STUB, "Stub I/O register read: %03x", address);
+		if (address >= REG_MAX) {
+			GBALog(gba, GBA_LOG_GAME_ERROR, "Read from unused I/O register: %03X", address);
+			return 0; // TODO: Reuse LOAD_BAD
+		}
 		break;
 	}
 	return gba->memory.io[address >> 1];