Notes: 2026-08-10 CoreCollective Windows on Arm Technical
Nathalie Chan King Choy
We have two primary paths forward:
1) Bring up native gfortran on aarch64-w64-mingw32. This would achieve full parity with x64, but it depends on upstreaming GCC's C++, SEH, and native compilation work.
2) Extend LLVM Flang to support the GNU ABI for Windows on Arm.
These approaches are not mutually exclusive, and we may pursue both.
We would like to gather the Flang community, toolchain vendors, and other stakeholders to properly scope the effort, map out dependencies for each path, identify who is currently blocked, and align on the best strategy moving forward."
Evgeny K.
Gleb K.
Grant L.
Jillian B.
Marcus P.
Nathalie C.
Omair J.
Rick D.
Saket J.
Thomas D.
Tyler M.
- https://omjavaid.github.io/wheels-on-arm/
- In Gleb's but not Omair's list: memray, oss2
- Evgeny's update on GCC:
- Upstreaming auto-import support for dynamic linking, which is important for the native toolchain.
- Removing unnecessary scripts before making the repository for weekly Windows builds public.
Meeting Overview
Welcome and introduction of new Arm participant Rick D. and Linaro staffing update.
Python ecosystem enablement, package tracker, Python 3.15 release status, and at-risk package identification.
Debugger maintenance (GDB/LLDB), LLVM performance optimization (PGO/ThinLTO), GCC updates, and repository management.
Decisions/Key Takeaways
[Deferred]GDB maintenance and testing on Windows on Arm is deprioritized and added to the backlog due to resource constraints and available alternatives (WinDbg, MSVC, LLDB).Python 3.15 on Windows on Arm meets minimum release requirements and is on track for an October launch.
Should try to transition non-engineering maintainer engagement for Python packages to scale teams (App Assure and AppReady).
Action Items
[Gleb K.]
Work with Omair J. to consolidate Python package tracking lists and identify critical path items.
Compile a shortlist of red-list at-risk packages (e.g., PyArrow, gRPCIO, CRC32) needing priority intervention.
[Marcus P.]
Connect with Rick D. to discuss engaging App Assure and AppReady teams for Python package maintainer outreach.
Follow up offline with Omair J. on LLVM PGO and ThinLTO performance upstreaming strategy and funding.
Coordinate cross-company marketing efforts (Microsoft, Arm, Qualcomm, Nvidia) for the Python on Windows on Arm release.
[Nathalie C.]
Distribute the prioritized project backlog list by email for offline review.
(DONE) Add Thomas D. as a collaborator the CoreCollective Windows on Arm GitHub repository upon receiving his GitHub ID.
(DONE - See email text above) Include Omair J.'s Flang integration write-up in the meeting notes and send a separate calendar invite for the next meeting.
[Omair J.]
Work with Gleb K. to merge Python package tracking data into a unified list.
Follow up offline with Marcus P. regarding LLVM PGO and ThinLTO testing and upstreaming.
[Rick D.]
Meet with Marcus P. to explore using App Assure and AppReady for package maintainer communication.
[Thomas D.]
Review the list of buildable Python packages to identify opportunities to accelerate enablement.
(DONE) Provide GitHub ID to Nathalie C. to receive collaborator access to the CoreCollective WoA WG repository.
Investigate potential team connections with Open3D.
For Future
Discuss Flang integration during the initial portion of the next meeting.
Notes
[Team Updates & Introductions]
Rick D. is on Arm's strategic developer and ecosystems team, Before that, he worked at Microsoft and GitHub. He is in WoA WG to focus on Python ecosystem partnerships.
Maxim Kuvyrkov has left Linaro; Windows on Arm technical topics will be managed by Omair J. and Mike H.
[Python Ecosystem & Package Trackers]
Omair J. created a "Wheels on Arm" GitHub tracker analyzing top packages, filtering pure vs. native Python, and applying a priority algorithm based on download count, AI/ML focus, and multi-platform availability.
Omair J. suggested submitting direct PRs for buildable packages beyond the top 1,000 during the remaining ~4 weeks prior to launch.
Gleb K. analyzed the second 1,000 packages for installability and source buildability, highlighting packages memray and oss2 that are not in Omair's list
Non-engineering outreach (maintainer communication and CI PRs) coudl be done by scale teams like App Assure and AppReady.
Steve Dower confirmed Python 3.15 for Windows on Arm is green for release, meeting minimum requirements with CI in place, targeting an October launch.
Cryptography support is restored in PR form and expected in the September release.
Gleb K. identified PyArrow, grpcio, and CRC32 as key at-risk/red-list packages needing priority focus.
[Debuggers (GDB & LLDB)]
GDB for Windows on Arm received initial upstream contributions in January, but Linaro is not currently testing or maintaining it.
WinDbg and MSVC debuggers remain viable alternatives for debugging on WoA.
LLDB is functional on Windows on Arm, but additional upstream maintenance and review resources are needed for new features like SVE and SME.
[LLVM Performance (PGO & ThinLTO)]
Marcus did a rough unofficial test applying PGO dataset from Linux and ThinLTO to Windows on Arm: LLVM builds demonstrated a 10-15% performance improvement.
Enabling ThinLTO within standard LLVM build constraints requires a more capable runner image to complete within 6 hours.
Linaro is preparing a report on Clang versus LLVM performance analysis as a follow-up to a presentation with Saket.
[GCC Updates & External Queries]
Arm is upstreaming auto-import support for dynamic linking to support native toolchains and preparing the repository for public weekly Windows builds.
Multiple external partners have expressed interest in GCC builds for Windows on Arm to Microsoft.
The team will inquire with AppReady and internal relationship teams regarding potential connections to Open3D.
[Repository Governance & Administration]
Nathalie C. is adding external collaborators the CoreCollective Windows on Arm WG repository. Let her know if the current permissions granted are not sufficient.
Project backlog prioritization list will be circulated via email for offline review.