[net11.0] CoreCLR R2R template builds fail for macCatalyst and on Windows

[mattleibow]

Description

CoreCLR R2R (ReadyToRun) template builds with UseMonoRuntime=false EnablePreviewFeatures=true fail to build for certain platform TFMs. The R2R compilation toolchain produces incorrect results or is missing entirely depending on the CI host OS.

This has been failing on every net11.0 branch CI build since the test was added on Jan 27, 2026.

Build Failures

macOS — macCatalyst R2R linker version mismatch

The R2R compiled object files target macCatalyst 15.2 but the linker expects the deployment target of 15.0:

ld : error : object file (.../net11.0-maccatalyst/maccatalyst-x64/R2R/Test.r2r.o) was built for newer 'macCatalyst' version (15.2) than being linked (15.0)
ld : error : object file (.../net11.0-maccatalyst/maccatalyst-arm64/R2R/Test.r2r.o) was built for newer 'macCatalyst' version (15.2) than being linked (15.0)

iOS and Android build fine on macOS — only macCatalyst is affected.

Windows — crossgen2 missing for Apple cross-compilation

The crossgen2 executable is not found when cross-compiling for iOS and macCatalyst on Windows:

error : The crossgen2 executable 'D:\...\packages\microsoft.netcore.app.crossgen2.win-x64\11.0.0-preview.2.26103.111/tools/crossgen2' does not exist.

Both iOS and macCatalyst TFMs fail to build. Android and Windows TFMs build fine. After the iOS/macCatalyst failures, the Windows job gets canceled after ~2 hours due to retry timeouts.

Platform Summary

TFM	macOS CI	Windows CI
Android	✅ Builds	✅ Builds
iOS	✅ Builds	❌ crossgen2 missing
macCatalyst	❌ R2R linker version mismatch	❌ crossgen2 missing
Windows	N/A	✅ Builds

Environment

• .NET SDK: 11.0.100-preview.2.26103.111
• iOS SDK: Microsoft.iOS.Sdk.net11.0_26.2 (26.2.11375-net11-p2)
• MacCatalyst SDK: Microsoft.MacCatalyst.Sdk.net11.0_26.2 (26.2.11375-net11-p2)

Impact

• Every net11.0 branch CI build fails (46/47 integration tests pass, this 1 fails)
• Windows integration test job times out and gets canceled (~2 hours wasted)

Workaround

PR #34304 works around this by removing the broken TFMs per platform:

• macOS: Removes macCatalyst → test validates R2R for Android + iOS
• Windows: Removes macCatalyst + iOS → test validates R2R for Android + Windows

The upstream fix is needed in the .NET SDK/runtime toolchain to:

1. Produce R2R images with correct macCatalyst deployment target metadata
2. Provide crossgen2 for Apple cross-compilation on Windows

[rolfbjarne]

ld : error : object file (.../net11.0-maccatalyst/maccatalyst-x64/R2R/Test.r2r.o) was built for newer 'macCatalyst' version (15.2) than being linked (15.0)
ld : error : object file (.../net11.0-maccatalyst/maccatalyst-arm64/R2R/Test.r2r.o) was built for newer 'macCatalyst' version (15.2) than being linked (15.0)

This is already fixed in dotnet/macios and dotnet/runtime: the minimum Mac Catalyst version will be 17.0.

#34237 should be the actual fix here.

error : The crossgen2 executable 'D:...\packages\microsoft.netcore.app.crossgen2.win-x64\11.0.0-preview.2.26103.111/tools/crossgen2' does not exist.

This is fixed in dotnet/macios for iOS. #34237 should be the fix here too.

It won't be possible to build Mac Catalyst remotely.