Add riscv64 (linux_riscv64) wheel to PyPI releases

[gounthar]

Add linux_riscv64 wheel to PyPI releases

Summary

pip install msgspec on riscv64 Linux currently requires building from source (~2 min on a 1.6 GHz RISC-V SoC). Adding linux_riscv64 to the wheel build matrix would give riscv64 users a prebuilt wheel.

Evidence

Tested wheel	msgspec-0.20.1.dev3+gf225b8fb3-cp313-cp313-linux_riscv64.whl
Hardware	BananaPi F3 (SpacemiT K1, rv64imafdcv, 8 cores @ 1.6 GHz, 16 GB RAM)
Python	3.13 (CPython)
Build system	cibuildwheel
Build time	~2 min (native, on hardware)

The wheel imports and passes basic smoke tests on riscv64 Linux.

Suggested CI change

Workflow: .github/workflows/build-wheels.yml

Add riscv64 matrix entry and QEMU step:

# In strategy.matrix, add:
- os: ubuntu-latest
  archs: riscv64

# Add QEMU step before cibuildwheel:
- name: Set up QEMU
  if: matrix.archs == 'riscv64'
  uses: docker/setup-qemu-action@v3
  with:
    platforms: riscv64

Ecosystem context

• manylinux_2_28_riscv64 images are available on quay.io/pypa/ (landed in pypa/manylinux, 2025)
• cibuildwheel 3.x supports riscv64 via QEMU emulation
• auditwheel supports riscv64 platform tags
• maturin-action supports riscv64gc-unknown-linux-gnu cross-compilation
• Packages already shipping riscv64 wheels on PyPI: aiohttp, yarl, regex, markupsafe, charset-normalizer, rpds-py, multidict, propcache, watchfiles, rignore, setproctitle
• RISC-V hardware is shipping: SiFive HiFive, SpacemiT K1/K3, Sophgo SG2044 (64-core)

Our temporary index

While upstream support is pending, we maintain a PEP 503 index with 50+ riscv64 wheels for the Python ML/AI stack, built natively on RISC-V hardware.

Tracking repo: https://github.com/gounthar/riscv64-python-wheels