# PatchDiffEngine (Binary Pre/Post Patch Comparison for Fix Verification)

## Module
BinaryIndex

## Status
IMPLEMENTED

## Description
Compares pre-patch and post-patch binaries at multiple levels (BasicBlock, CFG, StringRefs, Semantic/KSG fingerprints) to determine if a vulnerability has been remediated. Produces structured verification results with confidence scores based on match depth. Core verification logic for the Golden Set Diff Layer.

## Implementation Details
- **Modules**: `src/BinaryIndex/__Libraries/StellaOps.BinaryIndex.Diff/`, `src/BinaryIndex/__Libraries/StellaOps.BinaryIndex.Builders/`
- **Key Classes**:
  - `PatchDiffEngine` (`src/BinaryIndex/__Libraries/StellaOps.BinaryIndex.Diff/PatchDiffEngine.cs`) - core engine comparing pre/post binaries using `ISignatureMatcher`, `IFunctionFingerprintExtractor`, and `IFunctionDiffer`; produces `PatchDiffResult` with confidence scores
  - `PatchDiffEngine` (builders) (`src/BinaryIndex/__Libraries/StellaOps.BinaryIndex.Builders/PatchDiffEngine.cs`) - builder-level diff engine
  - `FunctionDiffer` (`src/BinaryIndex/__Libraries/StellaOps.BinaryIndex.Diff/FunctionDiffer.cs`) - function-level comparison with semantic analysis, call-graph edge diffing, and string reference comparison
  - `FunctionRenameDetector` (`src/BinaryIndex/__Libraries/StellaOps.BinaryIndex.Diff/FunctionRenameDetector.cs`) - detects renamed functions between versions
  - `VerdictCalculator` (`src/BinaryIndex/__Libraries/StellaOps.BinaryIndex.Diff/VerdictCalculator.cs`) - computes fix verification verdict from diff results
- **Models**: `PatchDiffResult`, `PatchDiffModels`, `DiffEvidenceModels`, `DiffOptions` (`src/BinaryIndex/__Libraries/StellaOps.BinaryIndex.Diff/Models/`)
- **Storage**: `IDiffResultStore`, `InMemoryDiffResultStore` (`src/BinaryIndex/__Libraries/StellaOps.BinaryIndex.Diff/Storage/`)
- **Source**: SPRINT_20260110_012_004_BINDEX_golden_set_diff_verify.md

## E2E Test Plan
- [ ] Submit pre-patch and post-patch binaries for a known CVE fix and verify the diff result shows patch applied
- [ ] Verify multi-level comparison: BasicBlock, CFG, StringRefs, and semantic fingerprints all contribute to confidence
- [ ] Verify `FunctionDiffer` with `IncludeSemanticAnalysis=true` computes semantic similarity
- [ ] Verify `FunctionRenameDetector` handles renamed functions between versions
- [ ] Verify `VerdictCalculator` produces correct verdict (Fixed, Vulnerable, Unknown) based on diff evidence
- [ ] Verify `NoPatchDetected` result is returned when binaries are identical
- [ ] Verify diff results are persistable via `IDiffResultStore` with content-addressed IDs