Add Windows ARM64 build and release support

.bazelrc

@@ -346,6 +346,15 @@ build:windows --enable_runfiles
 build:windows --extra_toolchains=@local_config_cc//:cc-toolchain-x64_windows-clang-cl
 build:windows --extra_execution_platforms=//:x64_windows-clang-cl
 
+# Windows ARM64 overrides: use the ARM64 platform instead of x64. The toolchain name is
+# auto-generated by local_config_cc – if this doesn't match what Bazel detects on the ARM64
+# runner, query @local_config_cc//:all to find the correct name.
+build:windows_arm64 --extra_toolchains=@local_config_cc//:cc-toolchain-arm64_windows-clang-cl
+build:windows_arm64 --extra_execution_platforms=//:arm64_windows-clang-cl
+# clang-cl on ARM64 Windows doesn't auto-link compiler-rt builtins, causing undefined symbols
+# like __udivti3 (128-bit integer division). Link the builtins library explicitly.
+build:windows_arm64 --linkopt=clang_rt.builtins-aarch64.lib
+
 # The Windows fastbuild bazel configuration is broken in that it necessarily generates PDB debug
 # information while the Linux and macOS toolchains only compile with debug information in the dbg
 # configuration or when requested with the -g flag. This causes huge increases in compile time and
@@ -435,6 +444,9 @@ build:release_windows --per_file_copt="src/workerd/server/container-client"@/cla
 # Work around Windows test failures in rpc-related tests
 build:release_windows --per_file_copt=src/workerd/io/worker-interface@/clang:-fno-inline
 
+build:release_windows_arm64 --config=release_windows
+build:release_windows_arm64 --config=windows_arm64
+
 build:windows --cxxopt='/std:c++23preview' --host_cxxopt='/std:c++23preview'
 build:windows --copt='/D_CRT_USE_BUILTIN_OFFSETOF' --host_copt='/D_CRT_USE_BUILTIN_OFFSETOF'
 build:windows --copt='/DWIN32_LEAN_AND_MEAN' --host_copt='/DWIN32_LEAN_AND_MEAN'

.github/actions/setup-runner/action.yml

@@ -49,6 +49,14 @@ runs:
         git config --show-scope --show-origin core.symlinks
         git config --system core.longpaths true
         [System.IO.File]::WriteAllLines((Join-Path -Path $env:USERPROFILE -ChildPath '.bazelrc'), 'startup --output_user_root=\\\\?\\C:\\tmp')
+    - name: Use Bazel 9.0.2rc1 on ARM64 Windows
+      shell: pwsh
+      if: runner.os == 'Windows' && runner.arch == 'ARM64'
+      # Bazel 9.0.1 has a broken ARM64 Windows build (bazelbuild/bazel#28941).
+      # Use 9.0.2rc1 which fixes the JNI DLL architecture mismatch.
+      # TODO(cleanup): Remove this once .bazelversion is bumped to 9.0.2+.
+      run: |
+        echo "USE_BAZEL_VERSION=9.0.2rc1" >> $env:GITHUB_ENV
     - name: Setup macOS
       if: runner.os == 'macOS'
       shell: bash

.github/workflows/release.yml

@@ -104,6 +104,11 @@ jobs:
             image: windows-2025-16core
             bazel-config: release_windows
             target-arch: X64
+          - title: windows-arm64
+            os-name: Windows
+            image: windows-11-arm
+            bazel-config: release_windows_arm64
+            target-arch: ARM64
     name: build (${{ matrix.title }})
     uses: './.github/workflows/_bazel.yml'
     with:
@@ -130,8 +135,6 @@ jobs:
     strategy:
       matrix:
         arch: [linux-64, darwin-64, windows-64]
-        # This variable itself is unused, but allows us to set up two macOS builds. arm64 builds for
-        # other platforms will be supported later, then we'll list both architectures here.
         cpu: [X64]
         include:
           - arch: linux-64
@@ -146,6 +149,9 @@ jobs:
             cpu: ARM64
           - arch: windows-64
             name: Windows-X64
+          - arch: windows-arm64
+            name: Windows-ARM64
+            cpu: ARM64
     steps:
       - name: Checkout Repo
         uses: actions/checkout@v6
@@ -158,15 +164,15 @@ jobs:
           name: ${{ matrix.name }}-binary
           path: /tmp
       # Set execute permissions before compressing the binary
-      - if: matrix.arch != 'windows-64'
+      - if: ${{ !contains(matrix.arch, 'windows') }}
         run: chmod +x /tmp/workerd
       - name: Compress release binary
         run: |
           # As of release v1.20230404.0 the Linux x64 binary after debug_strip is 65.8 MB,
           # 21.0 MB with gzip and 17.3 MB with brotli -9. Use gzip as a widely supported format
           # which still produces an acceptable compressed size.
-          gzip -9N -k /tmp/workerd${{ matrix.arch == 'windows-64' && '.exe' || '' }}
-      - run: mv /tmp/workerd${{ matrix.arch == 'windows-64' && '.exe' || '' }}.gz /tmp/workerd-${{ matrix.arch }}.gz
+          gzip -9N -k /tmp/workerd${{ contains(matrix.arch, 'windows') && '.exe' || '' }}
+      - run: mv /tmp/workerd${{ contains(matrix.arch, 'windows') && '.exe' || '' }}.gz /tmp/workerd-${{ matrix.arch }}.gz
       # Upload compressed release binaries – one set of artifacts is sufficient with gzip being
       # widely supported
       - name: Upload Release Assets
@@ -191,7 +197,7 @@ jobs:
           WORKERD_VERSION: ${{ needs.version.outputs.version }}
           LATEST_COMPATIBILITY_DATE: ${{ needs.version.outputs.date }}
       - run: mkdir npm/workerd-${{ matrix.arch }}/bin
-      - run: cp /tmp/workerd${{ matrix.arch == 'windows-64' && '.exe' || '' }} npm/workerd-${{ matrix.arch }}/bin/workerd${{ matrix.arch == 'windows-64' && '.exe' || '' }}
+      - run: cp /tmp/workerd${{ contains(matrix.arch, 'windows') && '.exe' || '' }} npm/workerd-${{ matrix.arch }}/bin/workerd${{ contains(matrix.arch, 'windows') && '.exe' || '' }}
       - run: echo '//registry.npmjs.org/:_authToken=${NPM_TOKEN}' > npm/workerd-${{ matrix.arch }}/.npmrc
       - run: cd npm/workerd-${{ matrix.arch }} && npm publish --access public --tag ${{ startsWith(needs.version.outputs.version, '0') && 'beta' || 'latest'}}
         env:

.github/workflows/test.yml

@@ -37,6 +37,7 @@ jobs:
             { name: linux-arm, arch: ARM64, image: ubuntu-22.04-arm-16core },
             { name: macOS, arch: ARM64, image: macos-15-xlarge, use_lld: true },
             { name: windows, arch: X64, image: windows-2025-16core },
+            { name: windows-arm64, arch: ARM64, image: windows-11-arm },
           ]
         config: [
             # Default build: no suffix or additional bazel arguments
@@ -57,6 +58,8 @@ jobs:
         exclude:
           - os: { name: windows, arch: X64, image: windows-2025-16core }
             config: { suffix: -debug }
+          - os: { name: windows-arm64, arch: ARM64, image: windows-11-arm }
+            config: { suffix: -debug }
           # due to resource constraints, exclude the macOS and x64 Linux debug runners for now.
           # linux-asan and arm64 linux-debug should provide sufficient coverage for building in the
           # debug configuration.

BUILD.bazel

@@ -62,6 +62,15 @@ platform(
     ],
 )
 
+platform(
+    name = "arm64_windows-clang-cl",
+    constraint_values = [
+        "@platforms//cpu:aarch64",
+        "@platforms//os:windows",
+        "@bazel_tools//tools/cpp:clang-cl",
+    ],
+)
+
 # Used for cross-compilation
 platform(
     name = "macOS_x86",

MODULE.bazel

@@ -35,6 +35,42 @@ archive_override(
 bazel_dep(name = "rules_go", version = "0.60.0", repo_name = None)
 bazel_dep(name = "rules_android", version = "0.7.1", repo_name = None)
 
+# Override yq.bzl to 0.3.5 for Windows ARM64 yq toolchain support. The transitive version (0.3.2)
+# pulled in by aspect_rules_js lacks windows_arm64 in its platform list.
+bazel_dep(name = "yq.bzl", version = "0.3.5")
+archive_override(
+    module_name = "yq.bzl",
+    integrity = "sha256-zma0n7LjdqDY0rxYe8GqIju96A6GwKghRXCYp56lgDg=",
+    strip_prefix = "yq.bzl-0.3.5",
+    url = "https://github.com/bazel-contrib/yq.bzl/releases/download/v0.3.5/yq.bzl-v0.3.5.tar.gz",
+)
+
+# Patch aspect_rules_js to add yq_windows_arm64 to its use_repo list. Without this, the
+# @yq_windows_arm64 repo created by yq.bzl is not visible from aspect_rules_js's module scope.
+archive_override(
+    module_name = "aspect_rules_js",
+    integrity = "sha256-eBgxR7xQutVxi+c7M4Dn9G4hR/PJl6KQ4sXpWZQQUuE=",
+    patch_args = ["-p1"],
+    patches = [
+        "//:patches/aspect_rules_js/0001-add-yq-windows-arm64-to-use-repo.patch",
+    ],
+    strip_prefix = "rules_js-3.0.3",
+    url = "https://github.com/aspect-build/rules_js/releases/download/v3.0.3/rules_js-v3.0.3.tar.gz",
+)
+
+# Patch aspect_rules_esbuild to add win32-arm64 platform + integrity hash. The upstream rules
+# don't include ARM64 Windows despite esbuild shipping native binaries for it.
+archive_override(
+    module_name = "aspect_rules_esbuild",
+    integrity = "sha256-tz1ly+0pGMOC93pUihBpgrQPhSAPAlVl1c+hsuCQEec=",
+    patch_args = ["-p1"],
+    patches = [
+        "//:patches/aspect_rules_esbuild/0001-add-win32-arm64-platform.patch",
+    ],
+    strip_prefix = "rules_esbuild-0.25.1",
+    url = "https://github.com/aspect-build/rules_esbuild/releases/download/v0.25.1/rules_esbuild-v0.25.1.tar.gz",
+)
+
 # Automatically managed dependencies
 include("//build/deps:gen/deps.MODULE.bazel")
 include("//build/deps:gen/build_deps.MODULE.bazel")

RELEASE.md

@@ -8,4 +8,4 @@ The primary distribution channel for `workerd` right now is through `npm`. We us
 
 ## Cutting Releases
 
-This is pretty simple, and completely automatic—every time the date in [release-version.txt](src/workerd/io/release-version.txt) changes, a new release is generated, along with the built binaries for `linux-64`, `linux-arm64`, `darwin-64`, `darwin-arm64` and `windows-64`. The types will also be generated and published automatically. This is governed by the [release.yml](.github/workflows/release.yml) GitHub Action.
+This is pretty simple, and completely automatic—every time the date in [release-version.txt](src/workerd/io/release-version.txt) changes, a new release is generated, along with the built binaries for `linux-64`, `linux-arm64`, `darwin-64`, `darwin-arm64`, `windows-64` and `windows-arm64`. The types will also be generated and published automatically. This is governed by the [release.yml](.github/workflows/release.yml) GitHub Action.

build/ci.bazelrc

@@ -88,12 +88,17 @@ test:ci-macOS --spawn_strategy=local
 build:ci-windows --config=release_windows
 build:ci-windows-debug --config=debug
 
+build:ci-windows-arm64 --config=release_windows_arm64
+
 # Some tests (like Python import tests) take a long time to run, especially when debug is enabled
 # For that reason, we only run them in the default configuration for each platform to minimize
 # effect on CI pipeline runtime.
 test:ci-linux --test_size_filters=
 test:ci-macOS --test_size_filters=
 test:ci-windows --test_size_filters=
+test:ci-windows-arm64 --test_size_filters=
+# The windows-11-arm runner has only 4 vCPUs (vs 16 for x64 Windows), so tests need more time.
+test:ci-windows-arm64 --test_timeout=15,60,240,240
 
 # Run container tests on Linux CI
 test:ci-linux --test_tag_filters=-off-by-default,-requires-fuzzilli

build/deps/rust.MODULE.bazel

@@ -8,6 +8,8 @@ RUST_TARGET_TRIPLES = [
     "x86_64-apple-darwin",
     # Add support for macOS rosetta
     "aarch64-unknown-linux-gnu",
+    # Add support for Windows ARM64
+    "aarch64-pc-windows-msvc",
 ]
 
 # rules_rust
@@ -36,6 +38,7 @@ rust.toolchain(
         "x86_64-pc-windows-msvc": ["-Ctarget-feature=+sse4.2"],
         "aarch64-unknown-linux-gnu": ["-Ctarget-feature=+crc"],
         # No options needed for aarch64-apple-darwin: CRC feature is enabled by default.
+        # No options needed for aarch64-pc-windows-msvc: CRC feature is enabled by default on ARM64.
     },
     extra_target_triples = RUST_TARGET_TRIPLES,
     rustfmt_version = RUST_NIGHTLY_VERSION,

deps/rust/BUILD.bazel

@@ -45,12 +45,22 @@ selects.config_setting_group(
     ],
 )
 
+selects.config_setting_group(
+    name = "win_arm64",
+    match_all = [
+        "@platforms//os:windows",
+        "@platforms//cpu:aarch64",
+    ],
+)
+
 CARGO_BAZEL = select({
     ":linux_x64": "@cargo_bazel_linux_x64//file:downloaded",
     ":linux_arm64": "@cargo_bazel_linux_arm64//file:downloaded",
     ":macos_x64": "@cargo_bazel_macos_x64//file:downloaded",
     ":macos_arm64": "@cargo_bazel_macos_arm64//file:downloaded",
     ":win_x64": "@cargo_bazel_win_x64//file:downloaded.exe",
+    # x64 cargo-bazel runs under emulation on Windows ARM64
+    ":win_arm64": "@cargo_bazel_win_x64//file:downloaded.exe",
 })
 
 # Generates a repository containing all the crates we reference from our
@@ -82,6 +92,7 @@ crates_vendor(
         "aarch64-unknown-linux-gnu",
         "x86_64-unknown-linux-gnu",
         "x86_64-pc-windows-msvc",
+        "aarch64-pc-windows-msvc",
     ],
 )
 

deps/rust/crates/BUILD.ahash-0.8.12.bazel

@@ -56,6 +56,9 @@ rust_library(
         "@rules_rust//rust/platform:x86_64-apple-darwin": [
             "@crates_vendor__once_cell-1.21.4//:once_cell",  # cfg(not(all(target_arch = "arm", target_os = "none")))
         ],
+        "@rules_rust//rust/platform:aarch64-pc-windows-msvc": [
+            "@crates_vendor__once_cell-1.21.4//:once_cell",  # cfg(not(all(target_arch = "arm", target_os = "none")))
+        ],
         "@rules_rust//rust/platform:x86_64-pc-windows-msvc": [
             "@crates_vendor__once_cell-1.21.4//:once_cell",  # cfg(not(all(target_arch = "arm", target_os = "none")))
         ],

deps/rust/crates/BUILD.jobserver-0.1.34.bazel

@@ -51,6 +51,9 @@ rust_library(
         "@rules_rust//rust/platform:x86_64-apple-darwin": [
             "@crates_vendor__libc-0.2.183//:libc",  # cfg(unix)
         ],
+        "@rules_rust//rust/platform:aarch64-pc-windows-msvc": [
+            "@crates_vendor__getrandom-0.3.4//:getrandom",  # cfg(windows)
+        ],
         "@rules_rust//rust/platform:x86_64-pc-windows-msvc": [
             "@crates_vendor__getrandom-0.3.4//:getrandom",  # cfg(windows)
         ],

deps/rust/crates/BUILD.mio-1.2.0.bazel

@@ -56,6 +56,9 @@ rust_library(
         "@rules_rust//rust/platform:x86_64-apple-darwin": [
             "@crates_vendor__libc-0.2.183//:libc",  # cfg(any(unix, target_os = "hermit", target_os = "wasi"))
         ],
+        "@rules_rust//rust/platform:aarch64-pc-windows-msvc": [
+            "@crates_vendor__windows-sys-0.61.2//:windows_sys",  # cfg(windows)
+        ],
         "@rules_rust//rust/platform:x86_64-pc-windows-msvc": [
             "@crates_vendor__windows-sys-0.61.2//:windows_sys",  # cfg(windows)
         ],

deps/rust/crates/BUILD.sha1-0.10.6.bazel

@@ -58,6 +58,9 @@ rust_library(
         "@rules_rust//rust/platform:x86_64-apple-darwin": [
             "@crates_vendor__cpufeatures-0.2.17//:cpufeatures",  # cfg(any(target_arch = "aarch64", target_arch = "x86", target_arch = "x86_64"))
         ],
+        "@rules_rust//rust/platform:aarch64-pc-windows-msvc": [
+            "@crates_vendor__cpufeatures-0.2.17//:cpufeatures",  # cfg(any(target_arch = "aarch64", target_arch = "x86", target_arch = "x86_64"))
+        ],
         "@rules_rust//rust/platform:x86_64-pc-windows-msvc": [
             "@crates_vendor__cpufeatures-0.2.17//:cpufeatures",  # cfg(any(target_arch = "aarch64", target_arch = "x86", target_arch = "x86_64"))
         ],

deps/rust/crates/BUILD.socket2-0.6.3.bazel

@@ -54,6 +54,9 @@ rust_library(
         "@rules_rust//rust/platform:x86_64-apple-darwin": [
             "@crates_vendor__libc-0.2.183//:libc",  # cfg(any(unix, target_os = "wasi"))
         ],
+        "@rules_rust//rust/platform:aarch64-pc-windows-msvc": [
+            "@crates_vendor__windows-sys-0.61.2//:windows_sys",  # cfg(windows)
+        ],
         "@rules_rust//rust/platform:x86_64-pc-windows-msvc": [
             "@crates_vendor__windows-sys-0.61.2//:windows_sys",  # cfg(windows)
         ],

deps/rust/crates/BUILD.termcolor-1.4.1.bazel

@@ -42,6 +42,9 @@ rust_library(
     ],
     version = "1.4.1",
     deps = select({
+        "@rules_rust//rust/platform:aarch64-pc-windows-msvc": [
+            "@crates_vendor__winapi-util-0.1.11//:winapi_util",  # cfg(windows)
+        ],
         "@rules_rust//rust/platform:x86_64-pc-windows-msvc": [
             "@crates_vendor__winapi-util-0.1.11//:winapi_util",  # cfg(windows)
         ],

deps/rust/crates/BUILD.tokio-1.50.0.bazel

@@ -37,6 +37,9 @@ rust_library(
         "socket2",
         "time",
     ] + select({
+        "@rules_rust//rust/platform:aarch64-pc-windows-msvc": [
+            "windows-sys",  # aarch64-pc-windows-msvc
+        ],
         "@rules_rust//rust/platform:x86_64-pc-windows-msvc": [
             "windows-sys",  # x86_64-pc-windows-msvc
         ],
@@ -69,6 +72,9 @@ rust_library(
         "@rules_rust//rust/platform:x86_64-apple-darwin": [
             "@crates_vendor__libc-0.2.183//:libc",  # x86_64-apple-darwin
         ],
+        "@rules_rust//rust/platform:aarch64-pc-windows-msvc": [
+            "@crates_vendor__windows-sys-0.61.2//:windows_sys",  # aarch64-pc-windows-msvc
+        ],
         "@rules_rust//rust/platform:x86_64-pc-windows-msvc": [
             "@crates_vendor__windows-sys-0.61.2//:windows_sys",  # x86_64-pc-windows-msvc
         ],

deps/rust/crates/BUILD.winapi-util-0.1.11.bazel

@@ -42,6 +42,9 @@ rust_library(
     ],
     version = "0.1.11",
     deps = select({
+        "@rules_rust//rust/platform:aarch64-pc-windows-msvc": [
+            "@crates_vendor__windows-sys-0.61.2//:windows_sys",  # cfg(windows)
+        ],
         "@rules_rust//rust/platform:x86_64-pc-windows-msvc": [
             "@crates_vendor__windows-sys-0.61.2//:windows_sys",  # cfg(windows)
         ],