rea/docs/go-binaries.md

Go binary build metadata

inspect_go_binary / inspect-go-binary answers which Go compiler version, modules, replacements and build settings are embedded in one selected local executable or library. It reads the file without running it and requires no Go installation, active binary target, Hopper, Ghidra or IDA.

rea inspect-go-binary /absolute/path/to/application --json

The CLI resolves relative paths against the caller's working directory. MCP requires an absolute filesystem path and preserves that exact selection:

{
  "name": "inspect_go_binary",
  "arguments": { "path": "/artifacts/application" }
}

Observations

The inline Evidence result contains the artifact path, SHA-256, byte length, container format, architecture, word size and byte order. A recognized build_info record contains:

• go_version, preserved as embedded UTF-8 text rather than forced into a semantic version, or null when the embedded bytes are not UTF-8;
• go_version_bytes_base64, preserving the exact compiler-string bytes;
• exact file offsets and byte lengths for the header, compiler string and module string;
• module_text, the decoded module-information body, or null when the complete body cannot be represented as UTF-8;
• module_bytes_base64, the original module-string bytes including Go framing;
• module.path, the embedded package path;
• module.main, the main module's path, version, checksum and optional replacement;
• module.dependencies, with the same fields and their original order;
• module.settings, retaining ordered key/value entries and duplicate keys;
• module.unparsed_lines, module.unparsed_line_bytes_base64 and module.complete, which says whether every present module-text line was parsed. It does not establish that the dependency inventory is complete.

Missing checksums are null; empty fields and development/local replacement versions remain unchanged. Build settings such as GOOS, GOARCH or vcs.revision are reported when present. Their absence does not establish a build choice. Go strings may contain arbitrary bytes. Non-UTF-8 records remain available as base64 while other decodable module records are still reported; the reader does not insert replacement characters or reject the entire artifact for those strings.

When no main-module (mod) record was decoded, module.main is null and dependency coverage is unknown. Successfully decoded dependency records remain visible. GOPATH-mode builds may contain only a package path and build settings; their empty dependency array does not establish the absence of dependencies. The result's limitations state this explicitly. A module-mode build with a main module record and no dependency records has an observed empty dependency list.

Supported boundary

The built-in TypeScript reader supports ELF, PE and thin Mach-O images with Go's inline or historical pointer build-info encoding. Source ranges refer to the original stable file snapshot, including pointer-backed strings. It does not scan arbitrary byte strings as compiler metadata or interpret a fat Mach-O container as one selected architecture.

For ELF images without a named build-info section, discovery checks each nonempty writable, non-executable load segment in program-header order. This includes sectionless PIE images with metadata in a later data segment. Named sections retain priority, and alignment, file mapping and record validation remain required.

Historical moduleless Go binaries can store their empty module-string header in declared zero-initialized virtual memory rather than file-backed bytes. The reader recognizes this only when the complete optional module header lies in that memory without a conflicting file mapping. Its module contents are empty and module_location has zero bytes, anchored at the build-info field containing the module-header pointer. Compiler strings and other unmapped pointers remain strict file-backed reads.

build_info: null means no recognized record was found in the inspected image. It does not prove that the binary is not Go. Stripping, old builds, deliberate removal and obfuscation can limit metadata. A malformed supported container or recognized build-info record returns an input-format failure. Unsupported containers receive a separate unsupported-target failure.

Symlinks and nonregular files are rejected. The shared stable reader detects replacement and observed in-place changes during acquisition. Missing files, host permission denial, changed artifacts and cancellation retain distinct errors. The selected file is never modified; this inspection creates no temporary files, starts no subprocesses and accesses no network endpoint.

An input above 256 MiB returns resource_constraint with resource file-size and reported_limits.maximum_input_bytes. Select a suitable input within that fixed allowance; changing an output-write or transport budget does not admit it.

Resource guards bound the selected file and cumulative header searches to 256 MiB each, aggregate embedded strings to 1 MiB, structural table decoding to 16 MiB and the complete normalized metadata report to 8 MiB. Identical search spans with the same virtual alignment are searched once; partially overlapping spans consume the cumulative search budget and fail with a CPU resource constraint when it is exhausted. Oversized results fail without partial success. MCP also applies its response transport budget, which counts both text and structured content; a report within the metadata limit can still require export from retained Evidence. These limits are not operating-system memory or CPU isolation.

Embedded metadata is evidence of file content. It does not authenticate a compiler, dependency, commit or supply chain, and it does not establish runtime behavior. Function names, source mappings, types and decompiled code are outside this tool's coverage. Use the native workflow when those questions require a disassembler.

Real producer verification

npm run verify:go:binary exercises compiler-built fixtures through the public CLI and MCP, comparing their metadata with Go's standard debug/buildinfo reader. The verification lane requires Go; normal inspection does not.