[Build Failure] Crossgen2 AccessViolationException in Dictionary<Utf8String,_>.FindValue during maccatalyst-arm64 R2R build

[AndyAyersMS]

Description

The maccatalyst-arm64 Release AllSubsets_CoreCLR_Smoke CI job intermittently fails during R2R compilation of test binaries with a crossgen2 crash:

Microsoft.NET.CrossGen.targets(497,5): error : Fatal error.
System.AccessViolationException: Attempted to read or write protected memory. This is often an indication that other memory is corrupt.
   at Internal.Text.Utf8String.GetHashCode()
   at System.Collections.Generic.Dictionary`2[[Internal.Text.Utf8String, ILCompiler.ReadyToRun, ...],[System.__Canon, ...]].FindValue(Internal.Text.Utf8String)
   at ILCompiler.ObjectWriter.ObjectWriter.GetUndefinedSymbols()
   at ILCompiler.ObjectWriter.ObjectWriter.EmitObject(System.IO.Stream, ...)
   at ILCompiler.DependencyAnalysis.ReadyToRunObjectWriter.EmitReadyToRunObjects(...)
   at ILCompiler.DependencyAnalysis.ReadyToRunObjectWriter.EmitObject(...)
   at ILCompiler.ReadyToRunCodegenCompilation.Compile(System.String)
   at ILCompiler.Program.RunSingleCompilation(...)
   at ILCompiler.Program.Run()
   at ILCompiler.Program.Main(System.String[])

Failing project: src/tests/FunctionalTests/iOS/Simulator/CoreCLR/iOS.CoreCLR.R2R.Test.csproj

Observed build: Build 1598031, job maccatalyst-arm64 Release AllSubsets_CoreCLR_Smoke, from PR #133915.

Environment / execution details

• This leg cross-compiles for maccatalyst-arm64 from an x64 host (CLR_CROSS_COMPONENTS_BUILD=1, -hostarch x64 -hostos osx).
• Crossgen2 runs self-contained, hosted by the bootstrap SDK 11.0.100-rc.1.26420.103 (downloaded from ci.dot.net) -- not a runtime built from the triggering PR. Only the cross-targeting JIT component (clrjit_unix_x64_arm64) used to emit the target arm64 code comes from the PR's own source tree.
• The crash is inside crossgen2's own process (ILCompiler.ObjectWriter), hashing symbol names in a Dictionary<Utf8String,_> while emitting R2R objects -- not in JIT-generated target code.

Evidence this is likely a transient/environment issue rather than a regression

• The same job succeeded on the immediately preceding CI run of the same PR (Build 1596791), whose source tree differed only by comment-only changes and one narrow JIT loop-cloning condition tweak unrelated to crossgen2's own hot paths.
• main branch builds around the same time also pass this job.
• AccessViolationException surfacing in generic dictionary/hash-code code is a classic signature of transient memory corruption (e.g., GC/JIT interaction, host environment issue) rather than a deterministic code defect.
• No known-issue match was found in Build Analysis for this exact stack trace, and no matching issue was found searching dotnet/runtime.

Additional occurrences

Reporter has observed what may be the same failure recurring in other, unrelated PR builds -- please check Build Analysis / this stack trace against other builds and link them here if they match.

Ask

Please advise if this is a known flake, or if further investigation (e.g., crash dump analysis) is warranted. Filing so it can be tracked/matched against future occurrences.

Note

This issue was drafted with AI assistance (GitHub Copilot).

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