Static analyzer automatically finds and fixes unwinnable states in Sierra SCI games

The tool changes how softlocks in Sierra games are handled by automatically detecting and patching them through static analysis. It decompiles the game binary, abstract-interprets the scripts into a graph of guarded room transitions, item movements, and plot-flag writes, then finds states where victory is impossible but input is still accepted. From that graph, it derives guards that block the dangerous crossings, verifies them against a guarded model, and compiles them into Sierra's own patch format.

Adopting this approach costs the need to recompile touched scripts and install patch files, but the originals are never modified and can be reverted by deleting the patches. The pipeline refuses to emit anything if guards fail verification or if a script will not compile, ensuring the patch is safe. It also treats demanding an impossible action as worse than the bug, so guards are placed where the player can still comply, such as refusing a crossing while holding a fatal item.

The analysis stops working when a death is avoidable from the current state; it distinguishes unwinnable states from avoidable deaths by reachability, not by death conditions. Some deaths are deliberately left in because they serve as hints, like the KGB beach death in Leisure Suit Larry 2. Additionally, certain games present harder problems, such as King's Quest V's village market, where matching payments to merchants becomes a matching problem that is still in progress.

The tool derives everything from the game's own code, start room, victory room, death signal, and debug flags, with no game-specific analysis code. It has been tested on four games spanning two engine eras, SCI0 and SCI1.1, showing the approach generalizes across the engine's major versions. This suggests a reusable pattern for static analysis and patching of legacy software beyond adventure games.