ci: add Windows cargo-xwin release PoC by bolinfest · Pull Request #20485 · openai/codex

bolinfest · 2026-04-30T19:04:11Z

Why

Windows release builds are currently expensive enough that the Windows jobs can dominate release latency. This PR is a proof of concept for building Windows release binaries from Linux with Cargo, using cargo-xwin to target x86_64-pc-windows-msvc.

The goal is to validate whether Cargo-based cross compilation can build the Windows release binaries we care about before changing the real signed release workflow. This PoC intentionally does not include signing logic.

What Changed

Adds .github/workflows/rust-release-windows-cross-compile-poc.yml, a minimal workflow that:

runs on ubuntu-24.04
installs the x86_64-pc-windows-msvc Rust target
installs cargo-xwin
caches Cargo registry/git data plus the xwin MSVC CRT and Windows SDK cache
builds these release binaries:
- codex-responses-api-proxy
- codex-app-server
- codex
verifies that the outputs are Windows PE32+ executables
uploads the binaries and Cargo timing HTML as workflow artifacts

Toolchain Confidence

This PoC is still a Cargo-based release build: the workflow runs cargo xwin build --release --target x86_64-pc-windows-msvc. It is not a Bazel build, and it is not changing the Rust target ABI away from the normal Windows MSVC target.

The important distinction from a native Windows cargo build --release --target x86_64-pc-windows-msvc is the host toolchain around Cargo:

native Windows builds typically use MSVC link.exe, an installed Visual Studio toolchain, and the installed Windows SDK
cargo-xwin uses xwin to provide the Microsoft CRT and Windows SDK headers/libs on non-Windows hosts
the cross build uses LLVM tooling, including lld-link; cargo-xwin defaults C/C++ cross-compilation to clang-cl

This is why the PoC verifies the produced files are normal Windows PE32+ executables for x86_64-pc-windows-msvc.

For linker maturity, this is not an obscure linker path. LLVM's Windows lld documentation says lld-link accepts almost all link.exe command-line options and is used to link production Windows builds of large real-world binaries such as Firefox and Chromium:

https://lld.llvm.org/windows_support.html

That does not mean Firefox or Chromium use cargo-xwin; the relevant point is that the linker family used by this cross-compilation path is already used for major production Windows binaries.

Relevant tool docs:

cargo-xwin: https://github.com/rust-cross/cargo-xwin
xwin: https://github.com/Jake-Shadle/xwin
LLVM lld-link: https://lld.llvm.org/windows_support.html

Before replacing the signed release path, we should still smoke-test the cross-built binaries on Windows and compare any relevant startup/runtime benchmarks. The main risks are compatibility or behavioral differences from lld-link, clang-cl, or SDK/CRT version differences, not a known systematic Rust runtime performance penalty from cross-compilation itself.

Workflow Commands

I triggered the successful thin-LTO workflow by pushing updates to the draft PR branch:

sl pr submit -d

That used the workflow's pull_request trigger.

I triggered the fat-LTO experiment with:

gh workflow run rust-release-windows-cross-compile-poc.yml \
  --repo openai/codex \
  --ref pr20485 \
  -f release_lto=fat

The build commands executed by the workflow are:

cargo xwin build \
  --release \
  --target "$WINDOWS_TARGET" \
  --timings \
  --bin codex-responses-api-proxy

cargo xwin build \
  --release \
  --target "$WINDOWS_TARGET" \
  --timings \
  --bin codex-app-server

cargo xwin build \
  --release \
  --target "$WINDOWS_TARGET" \
  --timings \
  --bin codex

For both successful runs, WINDOWS_TARGET was x86_64-pc-windows-msvc.

Verification

Successful thin-LTO workflow run:

https://github.com/openai/codex/actions/runs/25185982350

Successful thin-LTO job:

https://github.com/openai/codex/actions/runs/25185982350/job/73843273846

Per-binary build step timing from the successful thin-LTO run:

codex-responses-api-proxy: 1m59s
codex-app-server: 23m01s
codex: 16m03s
total job time: about 42m11s

Successful fat-LTO workflow run:

https://github.com/openai/codex/actions/runs/25190714066

Successful fat-LTO job:

https://github.com/openai/codex/actions/runs/25190714066/job/73859747064

Per-binary build step timing from the successful fat-LTO run:

codex-responses-api-proxy: 1m59s
codex-app-server: 25m01s
codex: 23m58s
total job time: about 54m30s

These are the durations of each sequential cargo xwin build step. Later build steps benefit from dependencies and artifacts produced by earlier steps in the same job.

The workflow verified these output files:

target/x86_64-pc-windows-msvc/release/codex-responses-api-proxy.exe
target/x86_64-pc-windows-msvc/release/codex-app-server.exe
target/x86_64-pc-windows-msvc/release/codex.exe

Downloading The Binaries

From the GitHub web UI:

Open the workflow run:
- thin LTO: https://github.com/openai/codex/actions/runs/25185982350
- fat LTO: https://github.com/openai/codex/actions/runs/25190714066
Scroll to the bottom of the run page.
In Artifacts, click windows-cross-compile-poc-x86_64-pc-windows-msvc-primary-app-server.

GitHub downloads the artifact as a .zip. You must be logged into GitHub and have access to the repo.

From the CLI:

gh run download 25185982350 \
  --repo openai/codex \
  --name windows-cross-compile-poc-x86_64-pc-windows-msvc-primary-app-server

gh run download 25190714066 \
  --repo openai/codex \
  --name windows-cross-compile-poc-x86_64-pc-windows-msvc-primary-app-server

Each artifact contains:

codex.exe
codex-app-server.exe
codex-responses-api-proxy.exe

Both artifacts expire on 2026-07-29.

## Status This is the Bazel PR-CI cross-compilation follow-up to #20485. It is intentionally split from the Cargo/cargo-xwin release-build PoC so #20485 can stay as the historical release-build exploration. The unrelated async-utils test cleanup has been moved to #20686, so this PR is focused on the Windows Bazel CI path. The intended tradeoff is now explicit in `.github/workflows/bazel.yml`: pull requests get the fast Windows cross-compiled Bazel test leg, while post-merge pushes to `main` run both that fast cross leg and a fully native Windows Bazel test leg. The native main-only job keeps full V8/code-mode coverage and gets a 40-minute timeout because it is less latency-sensitive than PR CI. All other Bazel jobs remain at 30 minutes. ## Why Windows Bazel PR CI currently does the expensive part of the build on Windows. A native Windows Bazel test job on `main` completed in about 28m12s, leaving very little headroom under the 30-minute job timeout and making Windows the slowest PR signal. #20485 showed that Windows cross-compilation can be materially faster for Cargo release builds, but PR CI needs Bazel because Bazel owns our test sharding, flaky-test retries, and integration-test layout. This PR applies the same high-level shape we already use for macOS Bazel CI: compile with remote Linux execution, then run platform-specific tests on the platform runner. The compromise is deliberately signal-aware: code-mode/V8 changes are rare enough that PR CI can accept losing the direct V8/code-mode smoke-test signal temporarily, while `main` still runs the native Windows job post-merge to catch that class of regression. A follow-up PR should investigate making the cross-built Windows gnullvm V8 archive pass the direct V8/code-mode tests so this tradeoff can eventually go away. ## What Changed - Adds a `ci-windows-cross` Bazel config that targets `x86_64-pc-windows-gnullvm`, uses Linux RBE for build actions, and keeps `TestRunner` actions local on the Windows runner. - Adds explicit Windows platform definitions for `windows_x86_64_gnullvm`, `windows_x86_64_msvc`, and a bridge toolchain that lets gnullvm test targets execute under the Windows MSVC host platform. - Updates the Windows Bazel PR test leg to opt into the cross-compile path via `--windows-cross-compile` and `--remote-download-toplevel`. - Adds a `test-windows-native-main` job that runs only for `push` events on `refs/heads/main`, uses the native Windows Bazel path, includes V8/code-mode smoke tests, and has `timeout-minutes: 40`. - Keeps fork/community PRs without `BUILDBUDDY_API_KEY` on the previous local Windows MSVC-host fallback, including `--host_platform=//:local_windows_msvc` and `--jobs=8`. - Preserves the existing integration-test shape on non-gnullvm platforms, while generating Windows-cross wrapper targets only for `windows_gnullvm`. - Resolves `CARGO_BIN_EXE_*` values from runfiles at test runtime, avoiding hard-coded Cargo paths and duplicate test runfiles. - Extends the V8 Bazel patches enough for the `x86_64-pc-windows-gnullvm` target and Linux remote execution path. - Makes the Windows sandbox test cwd derive from `INSTA_WORKSPACE_ROOT` at runtime when Bazel provides it, because cross-compiled binaries may contain Linux compile-time paths. - Keeps the direct V8/code-mode unit smoke tests out of the Windows cross PR path for now while native Windows CI continues to cover them post-merge. ## Command Shape The fast Windows PR test leg invokes the normal Bazel CI wrapper like this: ```shell ./.github/scripts/run-bazel-ci.sh \ --print-failed-action-summary \ --print-failed-test-logs \ --windows-cross-compile \ --remote-download-toplevel \ -- \ test \ --test_tag_filters=-argument-comment-lint \ --test_verbose_timeout_warnings \ --build_metadata=COMMIT_SHA=${GITHUB_SHA} \ -- \ //... \ -//third_party/v8:all \ -//codex-rs/code-mode:code-mode-unit-tests \ -//codex-rs/v8-poc:v8-poc-unit-tests ``` With the BuildBuddy secret available on Windows, the wrapper selects `--config=ci-windows-cross` and appends the important Windows-cross overrides after rc expansion: ```shell --host_platform=//:rbe --shell_executable=/bin/bash --action_env=PATH=/usr/bin:/bin --host_action_env=PATH=/usr/bin:/bin --test_env=PATH=${CODEX_BAZEL_WINDOWS_PATH} ``` The native post-merge Windows job intentionally omits `--windows-cross-compile` and does not exclude the V8/code-mode unit targets: ```shell ./.github/scripts/run-bazel-ci.sh \ --print-failed-action-summary \ --print-failed-test-logs \ -- \ test \ --test_tag_filters=-argument-comment-lint \ --test_verbose_timeout_warnings \ --build_metadata=COMMIT_SHA=${GITHUB_SHA} \ --build_metadata=TAG_windows_native_main=true \ -- \ //... \ -//third_party/v8:all ``` ## Research Notes The existing macOS Bazel CI config already uses the model we want here: build actions run remotely with `--strategy=remote`, but `TestRunner` actions execute on the macOS runner. This PR mirrors that pattern for Windows with `--strategy=TestRunner=local`. The important Bazel detail is that `rules_rs` is already targeting `x86_64-pc-windows-gnullvm` for Windows Bazel PR tests. This PR changes where the build actions execute; it does not switch the Bazel PR test target to Cargo, `cargo-nextest`, or the MSVC release target. Cargo release builds differ from this Bazel path for V8: the normal Windows Cargo release target is MSVC, and `rusty_v8` publishes prebuilt Windows MSVC `.lib.gz` archives. The Bazel PR path targets `windows-gnullvm`; `rusty_v8` does not publish a prebuilt Windows GNU/gnullvm archive, so this PR builds that archive in-tree. That Linux-RBE-built gnullvm archive currently crashes in direct V8/code-mode smoke tests, which is why the workflow keeps native Windows coverage on `main`. The less obvious Bazel detail is test wrapper selection. Bazel chooses the Windows test wrapper (`tw.exe`) from the test action execution platform, not merely from the Rust target triple. The outer `workspace_root_test` therefore declares the default test toolchain and uses the bridge toolchain above so the test action executes on Windows while its inner Rust binary is built for gnullvm. The V8 investigation exposed a Windows-client gotcha: even when an action execution platform is Linux RBE, Bazel can still derive the genrule shell path from the Windows client. That produced remote commands trying to run `C:\Program Files\Git\usr\bin\bash.exe` on Linux workers. The wrapper now passes `--shell_executable=/bin/bash` with `--host_platform=//:rbe` for the Windows cross path. The same Windows-client/Linux-RBE boundary also affected `third_party/v8:binding_cc`: a multiline genrule command can carry CRLF line endings into Linux remote bash, which failed as `$'\r'`. That genrule now keeps the `sed` command on one physical shell line while using an explicit Starlark join so the shell arguments stay readable. ## Verification Local checks included: ```shell bash -n .github/scripts/run-bazel-ci.sh bash -n workspace_root_test_launcher.sh.tpl ruby -e "require %q{yaml}; YAML.load_file(%q{.github/workflows/bazel.yml}); puts %q{ok}" RUNNER_OS=Linux ./scripts/list-bazel-clippy-targets.sh RUNNER_OS=Windows ./scripts/list-bazel-clippy-targets.sh RUNNER_OS=Linux ./tools/argument-comment-lint/list-bazel-targets.sh RUNNER_OS=Windows ./tools/argument-comment-lint/list-bazel-targets.sh ``` The Linux clippy and argument-comment target lists contain zero `*-windows-cross-bin` labels, while the Windows lists still include 47 Windows-cross internal test binaries. CI evidence: - Baseline native Windows Bazel test on `main`: success in about 28m12s, https://github.com/openai/codex/actions/runs/25206257208/job/73907325959 - Green Windows-cross Bazel run on the split PR before adding the main-only native leg: Windows test 9m16s, Windows release verify 5m10s, Windows clippy 4m43s, https://github.com/openai/codex/actions/runs/25231890068 - The latest SHA adds the explicit PR-vs-main tradeoff in `bazel.yml`; CI is rerunning on that focused diff. ## Follow-Up A subsequent PR should investigate making a cross-built Windows binary work with V8/code-mode enabled. Likely options are either making the Linux-RBE-built `windows-gnullvm` V8 archive correct at runtime, or evaluating whether a Bazel MSVC target/toolchain can reuse the same prebuilt MSVC `rusty_v8` archive shape that Cargo release builds already use.

## Status This is the Bazel PR-CI cross-compilation follow-up to openai#20485. It is intentionally split from the Cargo/cargo-xwin release-build PoC so openai#20485 can stay as the historical release-build exploration. The unrelated async-utils test cleanup has been moved to openai#20686, so this PR is focused on the Windows Bazel CI path. The intended tradeoff is now explicit in `.github/workflows/bazel.yml`: pull requests get the fast Windows cross-compiled Bazel test leg, while post-merge pushes to `main` run both that fast cross leg and a fully native Windows Bazel test leg. The native main-only job keeps full V8/code-mode coverage and gets a 40-minute timeout because it is less latency-sensitive than PR CI. All other Bazel jobs remain at 30 minutes. ## Why Windows Bazel PR CI currently does the expensive part of the build on Windows. A native Windows Bazel test job on `main` completed in about 28m12s, leaving very little headroom under the 30-minute job timeout and making Windows the slowest PR signal. openai#20485 showed that Windows cross-compilation can be materially faster for Cargo release builds, but PR CI needs Bazel because Bazel owns our test sharding, flaky-test retries, and integration-test layout. This PR applies the same high-level shape we already use for macOS Bazel CI: compile with remote Linux execution, then run platform-specific tests on the platform runner. The compromise is deliberately signal-aware: code-mode/V8 changes are rare enough that PR CI can accept losing the direct V8/code-mode smoke-test signal temporarily, while `main` still runs the native Windows job post-merge to catch that class of regression. A follow-up PR should investigate making the cross-built Windows gnullvm V8 archive pass the direct V8/code-mode tests so this tradeoff can eventually go away. ## What Changed - Adds a `ci-windows-cross` Bazel config that targets `x86_64-pc-windows-gnullvm`, uses Linux RBE for build actions, and keeps `TestRunner` actions local on the Windows runner. - Adds explicit Windows platform definitions for `windows_x86_64_gnullvm`, `windows_x86_64_msvc`, and a bridge toolchain that lets gnullvm test targets execute under the Windows MSVC host platform. - Updates the Windows Bazel PR test leg to opt into the cross-compile path via `--windows-cross-compile` and `--remote-download-toplevel`. - Adds a `test-windows-native-main` job that runs only for `push` events on `refs/heads/main`, uses the native Windows Bazel path, includes V8/code-mode smoke tests, and has `timeout-minutes: 40`. - Keeps fork/community PRs without `BUILDBUDDY_API_KEY` on the previous local Windows MSVC-host fallback, including `--host_platform=//:local_windows_msvc` and `--jobs=8`. - Preserves the existing integration-test shape on non-gnullvm platforms, while generating Windows-cross wrapper targets only for `windows_gnullvm`. - Resolves `CARGO_BIN_EXE_*` values from runfiles at test runtime, avoiding hard-coded Cargo paths and duplicate test runfiles. - Extends the V8 Bazel patches enough for the `x86_64-pc-windows-gnullvm` target and Linux remote execution path. - Makes the Windows sandbox test cwd derive from `INSTA_WORKSPACE_ROOT` at runtime when Bazel provides it, because cross-compiled binaries may contain Linux compile-time paths. - Keeps the direct V8/code-mode unit smoke tests out of the Windows cross PR path for now while native Windows CI continues to cover them post-merge. ## Command Shape The fast Windows PR test leg invokes the normal Bazel CI wrapper like this: ```shell ./.github/scripts/run-bazel-ci.sh \ --print-failed-action-summary \ --print-failed-test-logs \ --windows-cross-compile \ --remote-download-toplevel \ -- \ test \ --test_tag_filters=-argument-comment-lint \ --test_verbose_timeout_warnings \ --build_metadata=COMMIT_SHA=${GITHUB_SHA} \ -- \ //... \ -//third_party/v8:all \ -//codex-rs/code-mode:code-mode-unit-tests \ -//codex-rs/v8-poc:v8-poc-unit-tests ``` With the BuildBuddy secret available on Windows, the wrapper selects `--config=ci-windows-cross` and appends the important Windows-cross overrides after rc expansion: ```shell --host_platform=//:rbe --shell_executable=/bin/bash --action_env=PATH=/usr/bin:/bin --host_action_env=PATH=/usr/bin:/bin --test_env=PATH=${CODEX_BAZEL_WINDOWS_PATH} ``` The native post-merge Windows job intentionally omits `--windows-cross-compile` and does not exclude the V8/code-mode unit targets: ```shell ./.github/scripts/run-bazel-ci.sh \ --print-failed-action-summary \ --print-failed-test-logs \ -- \ test \ --test_tag_filters=-argument-comment-lint \ --test_verbose_timeout_warnings \ --build_metadata=COMMIT_SHA=${GITHUB_SHA} \ --build_metadata=TAG_windows_native_main=true \ -- \ //... \ -//third_party/v8:all ``` ## Research Notes The existing macOS Bazel CI config already uses the model we want here: build actions run remotely with `--strategy=remote`, but `TestRunner` actions execute on the macOS runner. This PR mirrors that pattern for Windows with `--strategy=TestRunner=local`. The important Bazel detail is that `rules_rs` is already targeting `x86_64-pc-windows-gnullvm` for Windows Bazel PR tests. This PR changes where the build actions execute; it does not switch the Bazel PR test target to Cargo, `cargo-nextest`, or the MSVC release target. Cargo release builds differ from this Bazel path for V8: the normal Windows Cargo release target is MSVC, and `rusty_v8` publishes prebuilt Windows MSVC `.lib.gz` archives. The Bazel PR path targets `windows-gnullvm`; `rusty_v8` does not publish a prebuilt Windows GNU/gnullvm archive, so this PR builds that archive in-tree. That Linux-RBE-built gnullvm archive currently crashes in direct V8/code-mode smoke tests, which is why the workflow keeps native Windows coverage on `main`. The less obvious Bazel detail is test wrapper selection. Bazel chooses the Windows test wrapper (`tw.exe`) from the test action execution platform, not merely from the Rust target triple. The outer `workspace_root_test` therefore declares the default test toolchain and uses the bridge toolchain above so the test action executes on Windows while its inner Rust binary is built for gnullvm. The V8 investigation exposed a Windows-client gotcha: even when an action execution platform is Linux RBE, Bazel can still derive the genrule shell path from the Windows client. That produced remote commands trying to run `C:\Program Files\Git\usr\bin\bash.exe` on Linux workers. The wrapper now passes `--shell_executable=/bin/bash` with `--host_platform=//:rbe` for the Windows cross path. The same Windows-client/Linux-RBE boundary also affected `third_party/v8:binding_cc`: a multiline genrule command can carry CRLF line endings into Linux remote bash, which failed as `$'\r'`. That genrule now keeps the `sed` command on one physical shell line while using an explicit Starlark join so the shell arguments stay readable. ## Verification Local checks included: ```shell bash -n .github/scripts/run-bazel-ci.sh bash -n workspace_root_test_launcher.sh.tpl ruby -e "require %q{yaml}; YAML.load_file(%q{.github/workflows/bazel.yml}); puts %q{ok}" RUNNER_OS=Linux ./scripts/list-bazel-clippy-targets.sh RUNNER_OS=Windows ./scripts/list-bazel-clippy-targets.sh RUNNER_OS=Linux ./tools/argument-comment-lint/list-bazel-targets.sh RUNNER_OS=Windows ./tools/argument-comment-lint/list-bazel-targets.sh ``` The Linux clippy and argument-comment target lists contain zero `*-windows-cross-bin` labels, while the Windows lists still include 47 Windows-cross internal test binaries. CI evidence: - Baseline native Windows Bazel test on `main`: success in about 28m12s, https://github.com/openai/codex/actions/runs/25206257208/job/73907325959 - Green Windows-cross Bazel run on the split PR before adding the main-only native leg: Windows test 9m16s, Windows release verify 5m10s, Windows clippy 4m43s, https://github.com/openai/codex/actions/runs/25231890068 - The latest SHA adds the explicit PR-vs-main tradeoff in `bazel.yml`; CI is rerunning on that focused diff. ## Follow-Up A subsequent PR should investigate making a cross-built Windows binary work with V8/code-mode enabled. Likely options are either making the Linux-RBE-built `windows-gnullvm` V8 archive correct at runtime, or evaluating whether a Bazel MSVC target/toolchain can reuse the same prebuilt MSVC `rusty_v8` archive shape that Cargo release builds already use.

github-actions · 2026-05-16T06:47:56Z

Closing this pull request because it has had no updates for more than 14 days. If you plan to continue working on it, feel free to reopen or open a new PR.

## Status This is the Bazel PR-CI cross-compilation follow-up to openai#20485. It is intentionally split from the Cargo/cargo-xwin release-build PoC so openai#20485 can stay as the historical release-build exploration. The unrelated async-utils test cleanup has been moved to openai#20686, so this PR is focused on the Windows Bazel CI path. The intended tradeoff is now explicit in `.github/workflows/bazel.yml`: pull requests get the fast Windows cross-compiled Bazel test leg, while post-merge pushes to `main` run both that fast cross leg and a fully native Windows Bazel test leg. The native main-only job keeps full V8/code-mode coverage and gets a 40-minute timeout because it is less latency-sensitive than PR CI. All other Bazel jobs remain at 30 minutes. ## Why Windows Bazel PR CI currently does the expensive part of the build on Windows. A native Windows Bazel test job on `main` completed in about 28m12s, leaving very little headroom under the 30-minute job timeout and making Windows the slowest PR signal. openai#20485 showed that Windows cross-compilation can be materially faster for Cargo release builds, but PR CI needs Bazel because Bazel owns our test sharding, flaky-test retries, and integration-test layout. This PR applies the same high-level shape we already use for macOS Bazel CI: compile with remote Linux execution, then run platform-specific tests on the platform runner. The compromise is deliberately signal-aware: code-mode/V8 changes are rare enough that PR CI can accept losing the direct V8/code-mode smoke-test signal temporarily, while `main` still runs the native Windows job post-merge to catch that class of regression. A follow-up PR should investigate making the cross-built Windows gnullvm V8 archive pass the direct V8/code-mode tests so this tradeoff can eventually go away. ## What Changed - Adds a `ci-windows-cross` Bazel config that targets `x86_64-pc-windows-gnullvm`, uses Linux RBE for build actions, and keeps `TestRunner` actions local on the Windows runner. - Adds explicit Windows platform definitions for `windows_x86_64_gnullvm`, `windows_x86_64_msvc`, and a bridge toolchain that lets gnullvm test targets execute under the Windows MSVC host platform. - Updates the Windows Bazel PR test leg to opt into the cross-compile path via `--windows-cross-compile` and `--remote-download-toplevel`. - Adds a `test-windows-native-main` job that runs only for `push` events on `refs/heads/main`, uses the native Windows Bazel path, includes V8/code-mode smoke tests, and has `timeout-minutes: 40`. - Keeps fork/community PRs without `BUILDBUDDY_API_KEY` on the previous local Windows MSVC-host fallback, including `--host_platform=//:local_windows_msvc` and `--jobs=8`. - Preserves the existing integration-test shape on non-gnullvm platforms, while generating Windows-cross wrapper targets only for `windows_gnullvm`. - Resolves `CARGO_BIN_EXE_*` values from runfiles at test runtime, avoiding hard-coded Cargo paths and duplicate test runfiles. - Extends the V8 Bazel patches enough for the `x86_64-pc-windows-gnullvm` target and Linux remote execution path. - Makes the Windows sandbox test cwd derive from `INSTA_WORKSPACE_ROOT` at runtime when Bazel provides it, because cross-compiled binaries may contain Linux compile-time paths. - Keeps the direct V8/code-mode unit smoke tests out of the Windows cross PR path for now while native Windows CI continues to cover them post-merge. ## Command Shape The fast Windows PR test leg invokes the normal Bazel CI wrapper like this: ```shell ./.github/scripts/run-bazel-ci.sh \ --print-failed-action-summary \ --print-failed-test-logs \ --windows-cross-compile \ --remote-download-toplevel \ -- \ test \ --test_tag_filters=-argument-comment-lint \ --test_verbose_timeout_warnings \ --build_metadata=COMMIT_SHA=${GITHUB_SHA} \ -- \ //... \ -//third_party/v8:all \ -//codex-rs/code-mode:code-mode-unit-tests \ -//codex-rs/v8-poc:v8-poc-unit-tests ``` With the BuildBuddy secret available on Windows, the wrapper selects `--config=ci-windows-cross` and appends the important Windows-cross overrides after rc expansion: ```shell --host_platform=//:rbe --shell_executable=/bin/bash --action_env=PATH=/usr/bin:/bin --host_action_env=PATH=/usr/bin:/bin --test_env=PATH=${CODEX_BAZEL_WINDOWS_PATH} ``` The native post-merge Windows job intentionally omits `--windows-cross-compile` and does not exclude the V8/code-mode unit targets: ```shell ./.github/scripts/run-bazel-ci.sh \ --print-failed-action-summary \ --print-failed-test-logs \ -- \ test \ --test_tag_filters=-argument-comment-lint \ --test_verbose_timeout_warnings \ --build_metadata=COMMIT_SHA=${GITHUB_SHA} \ --build_metadata=TAG_windows_native_main=true \ -- \ //... \ -//third_party/v8:all ``` ## Research Notes The existing macOS Bazel CI config already uses the model we want here: build actions run remotely with `--strategy=remote`, but `TestRunner` actions execute on the macOS runner. This PR mirrors that pattern for Windows with `--strategy=TestRunner=local`. The important Bazel detail is that `rules_rs` is already targeting `x86_64-pc-windows-gnullvm` for Windows Bazel PR tests. This PR changes where the build actions execute; it does not switch the Bazel PR test target to Cargo, `cargo-nextest`, or the MSVC release target. Cargo release builds differ from this Bazel path for V8: the normal Windows Cargo release target is MSVC, and `rusty_v8` publishes prebuilt Windows MSVC `.lib.gz` archives. The Bazel PR path targets `windows-gnullvm`; `rusty_v8` does not publish a prebuilt Windows GNU/gnullvm archive, so this PR builds that archive in-tree. That Linux-RBE-built gnullvm archive currently crashes in direct V8/code-mode smoke tests, which is why the workflow keeps native Windows coverage on `main`. The less obvious Bazel detail is test wrapper selection. Bazel chooses the Windows test wrapper (`tw.exe`) from the test action execution platform, not merely from the Rust target triple. The outer `workspace_root_test` therefore declares the default test toolchain and uses the bridge toolchain above so the test action executes on Windows while its inner Rust binary is built for gnullvm. The V8 investigation exposed a Windows-client gotcha: even when an action execution platform is Linux RBE, Bazel can still derive the genrule shell path from the Windows client. That produced remote commands trying to run `C:\Program Files\Git\usr\bin\bash.exe` on Linux workers. The wrapper now passes `--shell_executable=/bin/bash` with `--host_platform=//:rbe` for the Windows cross path. The same Windows-client/Linux-RBE boundary also affected `third_party/v8:binding_cc`: a multiline genrule command can carry CRLF line endings into Linux remote bash, which failed as `$'\r'`. That genrule now keeps the `sed` command on one physical shell line while using an explicit Starlark join so the shell arguments stay readable. ## Verification Local checks included: ```shell bash -n .github/scripts/run-bazel-ci.sh bash -n workspace_root_test_launcher.sh.tpl ruby -e "require %q{yaml}; YAML.load_file(%q{.github/workflows/bazel.yml}); puts %q{ok}" RUNNER_OS=Linux ./scripts/list-bazel-clippy-targets.sh RUNNER_OS=Windows ./scripts/list-bazel-clippy-targets.sh RUNNER_OS=Linux ./tools/argument-comment-lint/list-bazel-targets.sh RUNNER_OS=Windows ./tools/argument-comment-lint/list-bazel-targets.sh ``` The Linux clippy and argument-comment target lists contain zero `*-windows-cross-bin` labels, while the Windows lists still include 47 Windows-cross internal test binaries. CI evidence: - Baseline native Windows Bazel test on `main`: success in about 28m12s, https://github.com/openai/codex/actions/runs/25206257208/job/73907325959 - Green Windows-cross Bazel run on the split PR before adding the main-only native leg: Windows test 9m16s, Windows release verify 5m10s, Windows clippy 4m43s, https://github.com/openai/codex/actions/runs/25231890068 - The latest SHA adds the explicit PR-vs-main tradeoff in `bazel.yml`; CI is rerunning on that focused diff. ## Follow-Up A subsequent PR should investigate making a cross-built Windows binary work with V8/code-mode enabled. Likely options are either making the Linux-RBE-built `windows-gnullvm` V8 archive correct at runtime, or evaluating whether a Bazel MSVC target/toolchain can reuse the same prebuilt MSVC `rusty_v8` archive shape that Cargo release builds already use.

bolinfest force-pushed the pr20485 branch 27 times, most recently from 4e16a08 to 46dd952 Compare May 1, 2026 09:00

ci: add Windows cargo-xwin release PoC

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bolinfest force-pushed the pr20485 branch from 46dd952 to d58ad83 Compare May 1, 2026 09:14

bolinfest mentioned this pull request May 1, 2026

ci: cross-compile Windows Bazel tests #20585

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ci: add Windows cargo-xwin release PoC#20485

ci: add Windows cargo-xwin release PoC#20485
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bolinfest commented Apr 30, 2026 •

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