bytecodealliance · silesmo · Mar 31, 2026
diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
@@ -80,11 +80,9 @@ jobs:
         os: [ubuntu-latest, macos-latest, windows-latest]
         # moonbit removed from language matrix for now - causing CI failures
         lang: [c, rust, csharp, cpp, go]
-        exclude:
-          # For now csharp doesn't work on macos, so exclude it from testing.
-          - os: macos-latest
-            lang: csharp
     runs-on: ${{ matrix.os }}
+    env:
+      RUNTIMELAB_COMMIT: '4cac3ab5c8e97fda69c23dfca41ace964babc05e'
     steps:
     - uses: actions/checkout@v4
       with:
@@ -103,7 +101,14 @@ jobs:
       uses: actions/setup-dotnet@v4
       with:
         dotnet-version: '9.x'
-      if: matrix.lang == 'csharp'
+      if: matrix.lang == 'csharp' && runner.os != 'macOS'
+
+    - name: Setup .NET 10 (macOS)
+      uses: actions/setup-dotnet@v4
+      with:
+        dotnet-version: '10.x'
+        dotnet-quality: 'preview'
+      if: matrix.lang == 'csharp' && runner.os == 'macOS'
 
     - name: Setup Go
       uses: actions/setup-go@v5
@@ -125,6 +130,57 @@ jobs:
       shell: powershell
       if: matrix.os == 'windows-latest' && matrix.lang == 'moonbit'
 
+    # macOS C# requires locally-built ILC packages since no osx-arm64
+    # packages are published on NuGet.
+    - name: Cache runtimelab ILC packages
+      id: cache-runtimelab
+      uses: actions/cache@v4
+      with:
+        path: runtimelab-packages
+        key: runtimelab-macos-arm64-${{ env.RUNTIMELAB_COMMIT }}
+      if: runner.os == 'macOS' && matrix.lang == 'csharp'
+
+    - name: Install LLVM 18 for runtimelab build
+      if: runner.os == 'macOS' && matrix.lang == 'csharp' && steps.cache-runtimelab.outputs.cache-hit != 'true'
+      run: brew install llvm@18
+
+    - name: Checkout runtimelab
+      uses: actions/checkout@v4
+      with:
+        repository: dotnet/runtimelab
+        ref: ${{ env.RUNTIMELAB_COMMIT }}
+        path: runtimelab
+      if: runner.os == 'macOS' && matrix.lang == 'csharp' && steps.cache-runtimelab.outputs.cache-hit != 'true'
+
+    - name: Build runtimelab ILC packages
+      if: runner.os == 'macOS' && matrix.lang == 'csharp' && steps.cache-runtimelab.outputs.cache-hit != 'true'
+      run: |
+        cd runtimelab
+        ln -sf $WASI_SDK_PATH src/mono/wasi/wasi-sdk
+        mkdir -p src/mono/wasi/include
+
+        # Build wasi libs and packages
+        ./build.sh clr.aot+libs -c Release -a wasm -os wasi /p:NuGetAudit=false
+        ./build.sh nativeaot.packages -c Release -a wasm -os wasi /p:NuGetAudit=false
+
+        # Build host compiler, libs, WASM JIT, and packages
+        ./build.sh clr.aot -c Release /p:NuGetAudit=false
+        ./build.sh libs -c Release /p:NuGetAudit=false
+        LLVM_CMAKE_CONFIG_RELEASE=$(brew --prefix llvm@18)/lib/cmake/llvm \
+        src/coreclr/build-runtime.sh -arm64 -release -os osx -outputrid osx-arm64 -component llvmjit
+        cp artifacts/bin/coreclr/osx.arm64.Release/libclrjit_universal_llvm32_arm64.dylib artifacts/bin/coreclr/osx.arm64.Release/ilc-published/
+        cp artifacts/bin/coreclr/osx.arm64.Release/libjitinterface_arm64.dylib artifacts/bin/coreclr/osx.arm64.Release/ilc-published/
+        ./build.sh nativeaot.packages -c Release /p:NuGetAudit=false
+
+        mkdir -p ../runtimelab-packages
+        cp artifacts/packages/Release/Shipping/*.nupkg ../runtimelab-packages/
+
+    - name: Set ILC env vars for macOS C#
+      if: runner.os == 'macOS' && matrix.lang == 'csharp'
+      run: |
+        echo "ILC_VERSION=10.0.0-dev" >> $GITHUB_ENV
+        echo "ILC_PACKAGES_PATH=${{ github.workspace }}/runtimelab-packages" >> $GITHUB_ENV
+
     # Run all codegen tests for this language
     - run: |
         cargo run test --languages ${{ matrix.lang }} tests/codegen \

diff --git a/crates/csharp/src/csproj.rs b/crates/csharp/src/csproj.rs
@@ -1,5 +1,5 @@
 use anyhow::Result;
-use std::{fs, path::PathBuf};
+use std::{env, fs, path::PathBuf};
 
 use heck::ToUpperCamelCase;
 
@@ -103,21 +103,36 @@ impl CSProjectLLVMBuilder {
             let os = match std::env::consts::OS {
                 "windows" => "win",
                 "linux" => std::env::consts::OS,
+                "macos" => "osx",
                 other => todo!("OS {} not supported", other),
             };
 
+            let arch = match std::env::consts::ARCH {
+                "aarch64" => "arm64",
+                "x86_64" => "x64",
+                other => todo!("ARCH {} not supported", other),
+            };
+
+            let ilc_version = env::var("ILC_VERSION").unwrap_or_else(|_| "10.0.0-*".to_string());
+
             csproj.push_str(
                 &format!(
                     r#"
         <ItemGroup>
-            <PackageReference Include="Microsoft.DotNet.ILCompiler.LLVM" Version="10.0.0-*" />
-            <PackageReference Include="runtime.{os}-x64.Microsoft.DotNet.ILCompiler.LLVM" Version="10.0.0-*" />
+            <PackageReference Include="Microsoft.DotNet.ILCompiler.LLVM" Version="{ilc_version}" />
+            <PackageReference Include="runtime.{os}-{arch}.Microsoft.DotNet.ILCompiler.LLVM" Version="{ilc_version}" />
         </ItemGroup>"#),
             );
 
+            let local_source = match env::var("ILC_PACKAGES_PATH") {
+                Ok(path) => format!(r#"<add key="local-ilc" value="{path}" />"#),
+                Err(_) => String::new(),
+            };
+
             fs::write(
                 self.dir.join("nuget.config"),
-                r#"<?xml version="1.0" encoding="utf-8"?>
+                format!(
+                    r#"<?xml version="1.0" encoding="utf-8"?>
             <configuration>
                 <config>
                     <!-- Store the packages where they can be shared between tests -->
@@ -126,11 +141,12 @@ impl CSProjectLLVMBuilder {
                 <packageSources>
                 <!--To inherit the global NuGet package sources remove the <clear/> line below -->
                 <clear />
+                {local_source}
                 <add key="nuget" value="https://api.nuget.org/v3/index.json" />
                 <add key="dotnet-experimental" value="https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet-experimental/nuget/v3/index.json" />
-                <!--<add key="dotnet-experimental" value="C:\github\runtimelab\artifacts\packages\Debug\Shipping" />-->
               </packageSources>
-            </configuration>"#,
+            </configuration>"#
+                ),
             )?;
         }
 

diff --git a/crates/test/src/csharp.rs b/crates/test/src/csharp.rs
@@ -99,6 +99,7 @@ impl LanguageMethods for Csharp {
         let os = match std::env::consts::OS {
             "windows" => "win",
             "linux" => std::env::consts::OS,
+            "macos" => "osx",
             other => todo!("OS {} not supported", other),
         };