Consider replacing Fedora UB leg with something else

[mmitche]

The Fedora UB leg is failing with some regularity due to #5288. This issue requires some changes in non-.NET code. While this is being fixed, I think it would be good to replace the Fedora leg and increase the UB pass rate.

[akoeplinger]

I think another option could be to disable crossgen in the Fedora leg. We already do that for some platforms here: https://github.com/dotnet/dotnet/blob/0fd2fe318f82a5d107e92f2c357cffc28f37f16f/src/runtime/src/installer/pkg/sfx/Microsoft.NETCore.App/Microsoft.NETCore.App.Runtime.CoreCLR.sfxproj#L25-L27

[jkotas]

I think another option could be to disable crossgen in the Fedora leg. We already do that for some platforms here:

It may just move the intermittent crash somewhere else, depends on how lucky we are.

If you want reliable workaround for Fedora, it would be disabling DCLR_CMAKE_USE_SYSTEM_LIBUNWIND here: https://github.com/dotnet/dotnet/pull/1453/files#diff-345aa0e2ddf0e155beaba10f6f14b2f3d83749c9c5c6f2c40418db541d8efbf2R50 . It would replace the buggy system libunwind with our bundled version.

[MichaelSimons]

If you want reliable workaround for Fedora, it would be disabling DCLR_CMAKE_USE_SYSTEM_LIBUNWIND here: https://github.com/dotnet/dotnet/pull/1453/files#diff-345aa0e2ddf0e155beaba10f6f14b2f3d83749c9c5c6f2c40418db541d8efbf2R50 . It would replace the buggy system libunwind with our bundled version.

I had thought the same but something isn't adding up to me. The leg which hits this issue is not setting DCLR_CMAKE_USE_SYSTEM_LIBUNWIND. From runtime binlog:

Command line arguments = "/__w/1/s/.dotnet/sdk/10.0.100-preview.7.25371.101/MSBuild.dll -maxcpucount --verbosity:m -tlp:default=auto --property:TreatWarningsAsErrors=true --property:ContinuousIntegrationBuild=true --property:Configuration=Release --property:RepoRoot=/__w/1/s/src/runtime/ --property:Restore=true --property:Build=true --property:DotNetBuild=true --property:DotNetBuildSourceOnly=true --property:DotNetBuildFromVMR=true --property:Rebuild=false --property:Test=false --property:Pack=true --property:IntegrationTest=false --property:PerformanceTest=false --property:Sign=false --property:Publish=true --property:RestoreStaticGraphEnableBinaryLogger=true --property:BuildAllConfigurations=true --property:TargetOS=linux --property:TargetArchitecture=x64 --property:BuildArchitecture=x64 --property:CMakeArgs="" --property:TargetRid=fedora.41-x64 --property:OfficialBuildId=20250721.101 --property:DotNetPackageVersionPropsPath=/__w/1/s/artifacts/obj/PackageVersions/PackageVersions.runtime.props --property:SourceBuiltAssetsDir=/__w/1/s/artifacts/assets/Release/ --property:SourceBuiltAssetManifestsDir=/__w/1/s/artifacts/obj/manifests/Release/runtime/ --property:RepositoryName=runtime --property:RepositoryUrl=https://github.com/dotnet/dotnet --property:PreviouslySourceBuiltNupkgCacheDir=/__w/1/s/prereqs/packages/previously-source-built/ --property:ReferencePackageNupkgCacheDir=/__w/1/s/prereqs/packages/reference/ --property:TrackPrebuiltUsageReportDir=/__w/1/s/artifacts/log/Release/runtime/ --property:SourceBuiltShippingPackagesDir=/__w/1/s/artifacts/packages/Release/Shipping/runtime/ --property:SourceBuiltNonShippingPackagesDir=/__w/1/s/artifacts/packages/Release/NonShipping/runtime/ --property:SourceBuiltPdbArtifactsDir=/__w/1/s/artifacts/SymStore/Release/runtime/ --property:SourceBuiltArtifactsBasePath=/__w/1/s/ --property:UsingToolMicrosoftNetCompilers=false --property:PortableBuild=false --property:PortableTargetRid=linux-x64 --property:RepoOriginalSourceRevisionId=98b587ce895026e3cebec9510e8d4e6eaa403151 --property:DotNetBuildAllRuntimePacks=true --property:UseBootstrap=true --verbosity:minimal /m /nologo /clp:Summary /nr:false /warnaserror /__w/1/s/artifacts/source-built-sdks/Microsoft.DotNet.Arcade.Sdk/tools/Build.proj /bl:"/__w/1/s/src/runtime/artifacts/log/Release/Build.binlog" -tl:false -logger:/__w/1/s/artifacts/source-built-sdks/Microsoft.DotNet.Arcade.Sdk/tools/net/Microsoft.DotNet.ArcadeLogging.dll"

[jkotas]

The build tools do not run on live runtime - they run on the previously built runtime. The problem is in the previously built runtime. How was the previously built runtime created?

[MichaelSimons]

The build tools do not run on live runtime - they run on the previously built runtime. The problem is in the previously built runtime. How was the previously built runtime created?

Ok, that would explain why. The previously built runtime is using the system libs. I can change this in CI.