unionlabs/union · error

parsing rev

Error message

parsing rev

What it means

extract_elf reads the .note.embed_commit.GIT_REV ELF section and reinterprets its first size_of::<Rev>() (32) bytes as the Rev enum (discriminant for unknown/dirty plus a 20-byte hash). bytemuck's checked cast fails when those bytes are not a valid Rev bit pattern — typically an unknown discriminant byte — and the anyhow context "parsing rev" wraps the failure.

Source

Thrown at lib/embed-commit/verifier/src/lib.rs:38

///
/// This function will error if the elf binary bytes provided cannot be parsed, or if the embedded git rev cannot be parsed. If there is no embedded git rev then `Ok(None)` will be returned.
pub fn extract_elf(bz: &[u8]) -> Result<Option<Rev>> {
    let file = ElfBytes::<AnyEndian>::minimal_parse(bz).context("parsing elf file")?;

    let Some(section) = file
        .section_header_by_name(".note.embed_commit.GIT_REV")
        .context("reading GIT_REV note section")?
    else {
        return Ok(None);
    };

    let (bytes, _) = file
        .section_data(&section)
        .context("reading GIT_REV note section data")?;

    bytemuck::checked::try_from_bytes::<Rev>(&bytes[0..std::mem::size_of::<Rev>()])
        .map_err(|e| anyhow!(e.to_string()))
        .context("parsing rev")
        .map(|rev| Some(*rev))
}

/// Retrieve the git rev from the provided wasm binary bytes.
///
/// # Errors
///
/// This function will error if the wasm binary bytes provided cannot be parsed, or if the returned git rev cannot be parsed. If there is no `commit_hash` export then `Ok(None)` will be returned.
pub fn extract_wasm(bz: &[u8]) -> Result<Option<Rev>> {
    let engine = Engine::default();
    let module = Module::from_binary(&engine, bz)?;
    let mut linker = Linker::new(&engine);
    let mut store: Store<()> = Store::new(&engine, ());

    // stub all imports as they're unused when evaluating commit_hash
    for import in module.imports() {
        linker.func_new(
            import.module(),

View on GitHub (pinned to 031785bb6d)

Solutions

  1. Rebuild the artifact with the union embed-commit toolchain so the note is well-formed
  2. Confirm you are inspecting the intended binary and inspect the section: readelf -x .note.embed_commit.GIT_REV <file>
  3. Align the verifier's embed-commit crate version with the producer's
  4. Treat parse failure as 'unrecognized producer' and report the underlying PodCastError rather than retrying

Example fix

// before
bytemuck::checked::try_from_bytes::<Rev>(&bytes[0..std::mem::size_of::<Rev>()])
  .map_err(|e| anyhow!(e.to_string()))
  .context("parsing rev")

// after — distinguish truncation from an invalid bit pattern
let need = std::mem::size_of::<Rev>();
if bytes.len() < need {
  anyhow::bail!("GIT_REV note too short: {} < {need}; binary not built by embed-commit", bytes.len());
}
let rev = bytemuck::checked::try_from_bytes::<Rev>(&bytes[..need])
  .map_err(|e| anyhow!("invalid GIT_REV bit pattern ({e:?}); binary not built by embed-commit"))?
  .clone();
Defensive patterns

Strategy: validation

Validate before calling

// Validate the note before the checked cast
let need = std::mem::size_of::<Rev>();
if bytes.len() < need { /* too short: not an embed-commit ELF */ }
let tag = bytes[0]; // discriminant byte for the repr(u8) Rev layout
if tag > 2 { /* invalid discriminant: foreign or corrupted producer */ }

Type guard

fn as_rev(bytes: &[u8]) -> Option<Rev> {
    if bytes.len() < std::mem::size_of::<Rev>() {
        return None;
    }
    bytemuck::checked::try_from_bytes::<Rev>(&bytes[..std::mem::size_of::<Rev>()])
        .ok()
        .map(|r| *r)
}

Prevention

When it happens

Trigger: Verifying an ELF whose GIT_REV note section exists but was written by a different producer/version or is corrupted: an invalid tag byte, a section produced with a different Rev layout, or bytes garbled by post-build processing. (A section shorter than 32 bytes instead panics at slicing before reaching this error.)

Common situations: Binaries rebuilt or patched after the note was embedded; a different toolchain writing a same-named section; embed-commit version drift between the builder that embedded the note and the verifier parsing it.

Related errors

AI-assisted analysis of unionlabs/union@031785bb6d (2026-08-16). Data as JSON: /api/errors/f7baf9b1d3771c95. Report an issue: GitHub.