# CONTRACT-BUILDID-PROPAGATION-401: Build-ID and Code-ID Propagation

> **Status:** Published
> **Version:** 1.0.0
> **Published:** 2025-12-13
> **Owners:** Scanner Guild, Signals Guild, BE-Base Platform Guild
> **Unblocks:** SCANNER-BUILDID-401-035, SCANNER-INITROOT-401-036, and downstream tasks

## Overview

This contract defines how GNU build-id (ELF), PE GUID, and Mach-O UUID propagate through the reachability pipeline from Scanner to SBOM, Signals, and runtime facts. It ensures consistent identification of binaries across components for deterministic symbol resolution and replay.

---

## 1. Build-ID Sources and Formats

### 1.1 Per-Format Extraction

| Binary Format | Build-ID Source | Prefix | Example |
|---------------|-----------------|--------|---------|
| ELF | `.note.gnu.build-id` | `gnu-build-id:` | `gnu-build-id:5f0c7c3cab2eb9bc...` |
| PE (Windows) | Debug GUID from PE header | `pe-guid:` | `pe-guid:12345678-1234-1234-1234-123456789abc` |
| Mach-O | `LC_UUID` load command | `macho-uuid:` | `macho-uuid:12345678123412341234123456789abc` |

### 1.2 Canonical Format

```
build_id = "{prefix}{hex_lowercase}"
```

- Hex encoding: lowercase, no separators (except PE GUID retains dashes)
- Minimum length: 16 bytes (32 hex chars) for ELF/Mach-O
- PE GUID: Standard GUID format with dashes

### 1.3 Fallback When Build-ID Absent

When build-id is not present (stripped binaries, older toolchains):

```json
{
  "build_id": null,
  "build_id_fallback": {
    "method": "file_hash",
    "value": "sha256:...",
    "confidence": 0.7
  }
}
```

**Fallback chain:**
1. `file_hash` - SHA-256 of entire binary file (confidence: 0.7)
2. `code_section_hash` - SHA-256 of .text section (confidence: 0.6)
3. `path_hash` - SHA-256 of file path (confidence: 0.3, last resort)

---

## 2. Code-ID for Name-less Symbols

### 2.1 Purpose

`code_id` provides stable identification for symbols in stripped binaries where the symbol name is unavailable.

### 2.2 Format

```
code_id = "code:{lang}:{base64url_sha256}"
```

**Canonical tuple for binary symbols:**
```
{format}\0{build_id_or_file_hash}\0{section}\0{addr}\0{size}\0{code_block_hash}
```

### 2.3 Code Block Hash

For stripped functions, compute hash of the code bytes:

```
code_block_hash = "sha256:" + hex(SHA256(code_bytes[addr:addr+size]))
```

---

## 3. Cross-RID (Runtime Identifier) Mapping

### 3.1 Problem Statement

Different platform builds (linux-x64, win-x64, osx-arm64) of the same source code produce different binaries with different build-ids. Runtime facts from one platform must map to the correct binary variant.

### 3.2 Variant Group

Binaries from the same source are grouped by source digest:

```json
{
  "variant_group": {
    "source_digest": "sha256:...",
    "variants": [
      {
        "rid": "linux-x64",
        "build_id": "gnu-build-id:aaa...",
        "file_hash": "sha256:..."
      },
      {
        "rid": "win-x64",
        "build_id": "pe-guid:bbb...",
        "file_hash": "sha256:..."
      },
      {
        "rid": "osx-arm64",
        "build_id": "macho-uuid:ccc...",
        "file_hash": "sha256:..."
      }
    ]
  }
}
```

### 3.3 Runtime Fact Correlation

When Signals ingests runtime facts:

1. Extract `build_id` from runtime event
2. Look up variant group containing this build_id
3. Correlate with richgraph nodes having matching `build_id`
4. If no match, fall back to `code_id` + `code_block_hash` matching

---

## 4. SBOM Integration

### 4.1 CycloneDX 1.6 Properties

Build-ID propagates to SBOM via component properties:

```json
{
  "type": "library",
  "name": "libssl.so.3",
  "version": "3.0.11",
  "properties": [
    {"name": "stellaops:build-id", "value": "gnu-build-id:5f0c7c3c..."},
    {"name": "stellaops:code-id", "value": "code:binary:abc123..."},
    {"name": "stellaops:file-hash", "value": "sha256:..."}
  ]
}
```

### 4.2 SPDX 3.0 Integration

Build-ID maps to SPDX external references:

```json
{
  "spdxId": "SPDXRef-libssl",
  "externalRef": {
    "referenceCategory": "PERSISTENT-ID",
    "referenceType": "gnu-build-id",
    "referenceLocator": "gnu-build-id:5f0c7c3c..."
  }
}
```

---

## 5. Signals Runtime Facts Schema

### 5.1 Runtime Event with Build-ID

```json
{
  "event_type": "function_hit",
  "timestamp": "2025-12-13T10:00:00Z",
  "binary": {
    "path": "/usr/lib/x86_64-linux-gnu/libssl.so.3",
    "build_id": "gnu-build-id:5f0c7c3c...",
    "file_hash": "sha256:..."
  },
  "symbol": {
    "name": "SSL_read",
    "address": "0x12345678",
    "symbol_id": "sym:binary:..."
  },
  "context": {
    "pid": 12345,
    "container_id": "abc123..."
  }
}
```

### 5.2 Ingestion Endpoint

```
POST /signals/runtime-facts
Content-Type: application/x-ndjson
Content-Encoding: gzip

{"event_type":"function_hit","binary":{"build_id":"gnu-build-id:..."},...}
{"event_type":"function_hit","binary":{"build_id":"gnu-build-id:..."},...}
```

---

## 6. RichGraph Integration

### 6.1 Node with Build-ID

```json
{
  "id": "sym:binary:...",
  "symbol_id": "sym:binary:...",
  "lang": "binary",
  "kind": "function",
  "display": "SSL_read",
  "build_id": "gnu-build-id:5f0c7c3c...",
  "code_id": "code:binary:...",
  "code_block_hash": "sha256:...",
  "purl": "pkg:deb/debian/libssl3@3.0.11"
}
```

### 6.2 CAS Evidence Storage

```
cas://binary/
  by-build-id/{build_id}/       # Index by build-id
    graph.json                   # Associated graph
    symbols.json                 # Symbol table
  by-code-id/{code_id}/          # Index by code-id
    block.bin                    # Code block bytes
    disasm.json                  # Disassembly
```

---

## 7. Implementation Requirements

### 7.1 Scanner Changes

| Component | Change | Priority |
|-----------|--------|----------|
| ELF parser | Extract `.note.gnu.build-id` | P0 |
| PE parser | Extract Debug GUID | P0 |
| Mach-O parser | Extract `LC_UUID` | P0 |
| RichGraphBuilder | Populate `build_id` field on nodes | P0 |
| SBOM emitters | Add `stellaops:build-id` property | P1 |

### 7.2 Signals Changes

| Component | Change | Priority |
|-----------|--------|----------|
| Runtime facts ingestion | Parse and index `build_id` | P0 |
| Scoring service | Correlate by `build_id` then `code_id` | P0 |
| Store repository | Add `build_id` index | P1 |

### 7.3 CLI/UI Changes

| Component | Change | Priority |
|-----------|--------|----------|
| `stella graph explain` | Show build_id in output | P1 |
| UI symbol drawer | Display build_id with copy button | P1 |

---

## 8. Validation Rules

1. `build_id` must match regex: `^(gnu-build-id|pe-guid|macho-uuid):[a-f0-9-]+$`
2. `code_id` must match regex: `^code:[a-z]+:[A-Za-z0-9_-]+$`
3. When `build_id` is null, `build_id_fallback` must be present
4. `code_block_hash` required when `build_id` is null and symbol is stripped
5. Variant group `source_digest` must be consistent across all variants

---

## 9. Test Fixtures

Location: `tests/Binary/fixtures/build-id/`

| Fixture | Description |
|---------|-------------|
| `elf-with-buildid/` | ELF binary with GNU build-id |
| `elf-stripped/` | ELF stripped, fallback to code-id |
| `pe-with-guid/` | PE binary with Debug GUID |
| `macho-with-uuid/` | Mach-O binary with LC_UUID |
| `variant-group/` | Same source, multiple RIDs |

---

## 10. Related Contracts

- [richgraph-v1](./richgraph-v1.md) - Graph schema with build_id field
- [Binary Reachability](../reachability/binary-reachability-schema.md) - Binary evidence schema
- [Symbol Manifest](../specs/SYMBOL_MANIFEST_v1.md) - Symbol identification

---

## Changelog

| Version | Date | Author | Changes |
|---------|------|--------|---------|
| 1.0.0 | 2025-12-13 | Scanner Guild | Initial contract for build-id propagation |