# ELF Normalization and Delta Hashing

## Module
BinaryIndex

## Status
IMPLEMENTED

## Description
Low-entropy delta signatures over ELF segments with normalization (relocation zeroing, NOP canonicalization, jump table rewriting). Not yet implemented.

## What's Implemented
- **Delta Signature Infrastructure**: `src/BinaryIndex/__Libraries/StellaOps.BinaryIndex.DeltaSig/` - function-level delta signatures with V1 and V2 predicates exist
  - `DeltaSignatureGenerator` - generates delta signatures (function-level, not ELF-segment-level)
  - `DeltaSignatureMatcher` - matches delta signatures
  - `CfgExtractor` - extracts control flow graphs
  - `IrDiffGenerator` - IR-level diff generation
- **Binary Diff Engine**: `src/BinaryIndex/__Libraries/StellaOps.BinaryIndex.Diff/PatchDiffEngine.cs` - byte-level and function-level diffing
- **ELF Feature Extraction**: `ElfFeatureExtractor` (`src/BinaryIndex/__Libraries/StellaOps.BinaryIndex.Core/Services/`) - extracts Build-ID and section info from ELF binaries
- **Disassembly**: `B2R2DisassemblyPlugin`, `HybridDisassemblyService` - multi-backend disassembly infrastructure

## What's Missing
- ELF segment-level normalization (relocation zeroing to eliminate position-dependent bytes)
- NOP canonicalization (normalizing NOP sled variations across compilers)
- Jump table rewriting (normalizing indirect jump table entries)
- Low-entropy delta hashing over normalized ELF segments (currently delta-sig operates at function level, not segment level)
- Segment-aware normalization that handles .text, .rodata, .data sections separately

## Implementation Plan
- Add ELF segment normalization pass to `ElfFeatureExtractor` or new `ElfNormalizer` class
- Implement relocation zeroing: identify and zero-out position-dependent bytes (GOT/PLT entries, absolute addresses)
- Implement NOP canonicalization: normalize all NOP variants to canonical form
- Implement jump table rewriting: normalize indirect jump table entries
- Add segment-level delta hashing on normalized output
- Integrate with existing `DeltaSignatureGenerator` for hybrid function+segment signatures
- Add tests using known ELF binaries with position-dependent variations

## Related Documentation
- Current delta-sig: `src/BinaryIndex/__Libraries/StellaOps.BinaryIndex.DeltaSig/`
- ELF extraction: `src/BinaryIndex/__Libraries/StellaOps.BinaryIndex.Core/Services/ElfFeatureExtractor.cs`
- Disassembly: `src/BinaryIndex/__Libraries/StellaOps.BinaryIndex.Disassembly.B2R2/`