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[Mono] mini-llvm.c build failure: LLVMMono1CallConv undeclared after LLVM SDK version bump to 26159.1 #125769

@kotlarmilos

Description

@kotlarmilos

Build Information

Build: https://dev.azure.com/dnceng-public/public/_build/results?buildId=1342414&view=results
Build error leg or test failing: tvos-arm64 Release AllSubsets_Mono
Pull request: #125556

Error Message

Fill the error message using step by step known issues guidance.

{
  "ErrorMessage": "error: use of undeclared identifier 'LLVMMono1CallConv'",
  "ErrorPattern": "",
  "BuildRetry": false,
  "ExcludeConsoleLog": false
}

The tvOS/iOS cross-compiler build fails with use of undeclared identifier 'LLVMMono1CallConv' in mini-llvm.c after the Mono LLVM SDK package version bump to 19.1.0-alpha.1.26159.1. In the dotnet/llvm-project the macOS SDK package appears to have been built with Homebrew LLVM 18 instead of AppleClang, because llvm.proj specifies the compiler as bare clang which resolves to /usr/local/bin/clang.

Similar to #125763

Known issue validation

Build: 🔎 https://dev.azure.com/dnceng-public/public/_build/results?buildId=1342414
Error message validated: [error: use of undeclared identifier 'LLVMMono1CallConv']
Result validation: ✅ Known issue matched with the provided build.
Validation performed at: 3/19/2026 11:29:41 AM UTC

Report

Build Definition Step Name Console log Pull Request
1343113 dotnet/runtime Build product Log #125732
1343078 dotnet/runtime Build product Log #121223
1343075 dotnet/runtime Build product Log #125774
1343072 dotnet/runtime Build product Log #125768
1343011 dotnet/runtime Build product Log #125772
1342977 dotnet/runtime Build product Log #125771
1342756 dotnet/runtime Build product Log #115996
1342966 dotnet/runtime Build product Log #122950
1342934 dotnet/runtime Build product Log #125441
1342906 dotnet/runtime Build product Log #124266
1342879 dotnet/runtime Build product Log #124648
1342889 dotnet/runtime Build product Log #125439
1342882 dotnet/runtime Build product Log #123209
1342876 dotnet/runtime Build product Log #124650
1342852 dotnet/runtime Build product Log #125437
1342845 dotnet/runtime Build product Log #124544
1340985 dotnet/runtime Build product Log #125603
1342794 dotnet/runtime Build product Log #125507
1342725 dotnet/runtime Build product Log #125656
1342672 dotnet/runtime Build product Log #125703
1342414 dotnet/runtime Build product Log

Summary

24-Hour Hit Count 7-Day Hit Count 1-Month Count
21 21 21

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    Known Build ErrorUse this to report build issues in the .NET Helix tabarea-Build-monoblocking-clean-ciBlocking PR or rolling runs of 'runtime' or 'runtime-extra-platforms'os-iosApple iOS

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