logos-blockchain-circuits/CONTRIBUTING.md

Contributor's Guide

Development Setup

Prerequisites

• Rust — the pinned toolchain version is in rust-toolchain.toml and will be installed automatically by rustup.
• pre-commit — used to run formatting, linting, and audit checks before each commit.

Installing the Pre-Commit Hooks

pre-commit install

This only needs to be done once after cloning the repo. Hooks will then run automatically on git commit.

Running Checks Manually

To run all hooks manually against all files:

pre-commit run --all-files

Maintenance

Rust Toolchain

When bumping the stable toolchain, update channel in rust-toolchain.toml. The comment there lists every other place that must be updated in sync (nightly version, CI workflows, pre-commit hooks).

Tool Versions

taplo, cargo-deny, and cargo-machete are pinned in two places that must stay in sync:

• .pre-commit-config.yaml (hook rev)
• .github/workflows/lint.yml (cargo install --version)

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Symbol Isolation in Circuit Libraries

Each circuit (PoQ, PoL, PoC, Signature) is compiled into a static archive (libpoq.a, libpol.a, etc.). All four archives share the same internal C++ runtime — loadCircuit, get_size_of_witness, the fr_* field arithmetic functions, calcwit_* functions, and others. They are compiled from the same source files but with different constant values per circuit (e.g. get_size_of_witness() returns 18149 for PoQ and 20531 for PoL).

The Problem

When two or more circuit libraries are linked into the same binary, the GNU linker silently picks the first definition it encounters for each symbol and discards the rest. No error, no warning. The result is that one circuit's constants end up hardwired into functions shared by both circuits, corrupting witness parsing. In practice: the wrong get_size_of_witness() value causes loadCircuit to compute an incorrect buffer size, pu32 walks off the end of the buffer, reads garbage as a length field, and the subsequent memcpy reads past the stack guard page, which results in a SIGSEGV.

The Fix

The Makefile's $(LIB) rule uses a two-step process on Linux and Windows to localize all internal symbols before archiving:

1. Partial link (ld -r): merges all .o files into a single relocatable object without producing a final executable. No symbols are resolved yet; this is consolidation only.
2. Symbol localization (objcopy --keep-global-symbol): demotes every global symbol to local except the circuit's two public FFI entry points. Local symbols are invisible to the final linker, so each archive retains a private copy of every internal symbol. This means no conflict is possible regardless of how many circuits are linked together.

The public symbols are derived automatically from PROJECT: a circuit built with PROJECT=poq keeps poq_generate_witness and poq_generate_witness_from_files global and localizes everything else.

To skip localization for a specific build (e.g. for debugging), pass PUBLIC_SYMBOLS= explicitly on the make command line.

On macOS, localization is skipped because objcopy is a GNU Binutils tool unavailable by default there. This is safe: macOS uses a two-level namespace by default, meaning symbols are qualified by which library they come from, so the conflict does not arise.

Maintenance

PUBLIC_SYMBOLS defaults to $(PROJECT)_generate_witness and $(PROJECT)_generate_witness_from_files. If the public FFI API ever changes, meaning the entrypoints are renamed or new ones added, the Makefile default must be updated, otherwise the affected symbols will be localized and linking will fail.

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Triggering a New Release for Logos Blockchain Circuits

To trigger a release build:

1. Create and push a tag in the format vX.Y.Z.
2. This will automatically trigger the .github/workflows/build_circuits.yml workflow.
3. Once the workflow finishes, the generated artifacts will be attached to a new release.

Currently, releases published this way are marked as Draft and Pre-Release to ensure that the changelog and pre-release steps are manually reviewed first.

Generated Artifacts

Each release includes a single unified bundle per platform:

Unified Release Bundles

For each supported platform (Linux x86_64, macOS aarch64, Windows x86_64):

• logos-blockchain-circuits-{version}-{os}-{arch}.tar.gz

  A complete bundle containing all components needed to generate and verify proofs for all circuits.

Bundle Structure:

logos-blockchain-circuits-{version}-{os}-{arch}/
├── VERSION
├── prover[.exe]
├── verifier[.exe]
├── pol/
│   ├── libpol.a
│   ├── witness_generator.dat
│   ├── include/
│   ├── proving_key.zkey
│   └── verification_key.json
├── poq/
│   ├── libpoq.a
│   ├── witness_generator.dat
│   ├── include/
│   ├── proving_key.zkey
│   └── verification_key.json
├── signature/
│   ├── libsignature.a
│   ├── witness_generator.dat
│   ├── include/
│   ├── proving_key.zkey
│   └── verification_key.json
└── poc/
    ├── libpoc.a
    ├── witness_generator.dat
    ├── include/
    ├── proving_key.zkey
    └── verification_key.json

On Windows, static libraries use the .lib extension instead of .a (e.g. pol.lib).

At the root level:

• prover: Rapidsnark prover binary for generating zk-SNARK proofs
• verifier: Rapidsnark verifier binary for verifying proofs

Each circuit directory contains:

• lib{circuit}.a / {circuit}.lib: Static library for generating witnesses from inputs
• witness_generator.dat: Required data file for the witness generator
• include/: C headers for linking against the witness generator library
• proving_key.zkey: Groth16 proving key for generating zk-SNARK proofs
• verification_key.json: Verification key for verifying proofs

The proving keys are generated using the Hermez Powers of Tau ceremony (powersOfTau28_hez_final_17.ptau), which supports circuits with up to 2^17 constraints.

Example

git tag v1.2.3 -m "Release v1.2.3"
git push --tags

Publishing the Release

After triggering the release, it will appear as a Draft and Pre-Release.
Before making it public, make sure to:

1. Review the changelog
   Ensure that all relevant changes are clearly listed and properly formatted.

2. Confirm the pre-release checklist
   Verify that all required steps have been completed, then remove the checklist from the release notes.

Once everything looks good:

3. Mark the release as published
   • Uncheck “This is a pre-release.”
   • Publish the release (removing the Draft state).

⚡ Important: Logos Blockchain builds will only pick up the new circuits once the release is published as Latest (i.e. not marked as draft or pre-release).