[ci-scan] Build break: Mono MiniFullAot AOT compile of JIT/Regression_ro_2 exits with code 134

[github-actions]

Build Information

Build: https://dev.azure.com/dnceng-public/public/_build/results?buildId=1603402
Build error leg or test failing: linux-x64 Release AllSubsets_Mono_MiniFullAot_RuntimeTests minifullaot-AOT compile CoreCLR tests

KBE authoring guidance (ci-failure-scan)

• Error Details is for readers. Paste the full exception, stack trace, or build error excerpt so the failure is understandable without opening the raw log.
• Build Analysis parses only the single JSON block under Error Message.
• ErrorMessage is a case-sensitive ordinal String.Contains substring copied verbatim from the failing log.
• Set BuildRetry to true only for a clear infrastructure retry case. ExcludeConsoleLog disables Helix console-log scanning.

Error Details

The AOT compile CoreCLR tests task on the linux-x64 Release AllSubsets_Mono_MiniFullAot_RuntimeTests minifullaot leg fails while AOT-compiling the JIT/Regression_ro_2 runtime test. The Mono AOT compiler aborts with exit code 134 (SIGABRT), breaking the test build for the whole leg:

/__w/1/s/src/mono/msbuild/aot-compile.proj(19,9): error MSB3073: The command "/__w/1/s/artifacts/tests/coreclr/linux.x64.Release/Tests/Core_Root/corerun /__w/1/s/artifacts/tests/coreclr/linux.x64.Release/JIT/Regression_ro_2/Regression_ro_2/Regression_ro_2.dll" exited with code 134.
Build FAILED.
    1 Error(s)
Build failed with exit code 1.

Reproduced in source build 1603402 (2026-09-19) and follow-up build 1603968 (2026-09-20); the leg was passing this task in builds prior to 1603402.

Error Message

{
  "ErrorMessage": "JIT/Regression_ro_2/Regression_ro_2/Regression_ro_2.dll\" exited with code 134.",
  "ErrorPattern": "",
  "BuildRetry": false,
  "ExcludeConsoleLog": false
}

Agentic workflow metadata (ci-failure-scan)

Workflow artifact: ci-failure-scan
Artifact kind: kbe-verification
Verified match count: 2 hits in failure.log

---

Filed by ci-failure-scan (detection only). ci-failure-fix walks open [ci-scan] KBEs and either opens a small fix PR or comments here to loop in owners — it never disables the test.

Generated by CI Outer-Loop Failure Scanner · opus48 · 831.7 AIC · ⌖ 14.9 AIC · ⊞ 19.2K · ◷

Report

Build	Repository	Step Name	Console log	Pull Request
1615702	dotnet/runtime	AOT compile CoreCLR tests	Log
1615485	dotnet/runtime	AOT compile CoreCLR tests	Log	#134819
1614142	dotnet/runtime	AOT compile CoreCLR tests	Log
1613653	dotnet/runtime	AOT compile CoreCLR tests	Log
1613174	dotnet/runtime	AOT compile CoreCLR tests	Log
1612276	dotnet/runtime	AOT compile CoreCLR tests	Log	#133197
1611740	dotnet/runtime	AOT compile CoreCLR tests	Log
1610154	dotnet/runtime	AOT compile CoreCLR tests	Log
1608288	dotnet/runtime	AOT compile CoreCLR tests	Log
1606626	dotnet/runtime	AOT compile CoreCLR tests	Log
1604459	dotnet/runtime	AOT compile CoreCLR tests	Log

Summary

24-Hour Hit Count	7-Day Hit Count	1-Month Count
2	9	11

[github-actions]

Workflow artifact: ci-fix
Artifact kind: handoff
Linked KBE: #134301

Note

AI/Copilot-generated triage note.

This Known Build Error has no producible automated code change (reason: Mono JIT/AOT codegen assertion — must not be auto-fixed), so I could not open even a best-effort PR. Looping in owners so it can be fixed forward rather than muted.

Root cause (best analysis)

The linux-x64 Release AllSubsets_Mono_MiniFullAot_RuntimeTests minifullaot leg aborts while Mono AOT-compiles JIT/Regression_ro_2/Regression_ro_2.dll. The latest failure log reports:

Assertion at src/mono/mono/mini/mini-amd64.c:5347, condition `amd64_is_imm32 (ins->inst_imm)` not met
Got a SIGABRT while executing native code.

The subsequent aot-compile.proj MSB3073 exit-code-134 error is only the build wrapper surfacing that compiler abort. This requires a Mono AMD64 instruction-emission/codegen correction; changing the test or its build wiring would only mask the product defect.

Evidence

• Failing build: 1606626
• First build it occurred: 1603402 — 2026-09-19 UTC; first observed in the scanned window
• Possible related PR: none identified with sufficient confidence

Suggested reviewers / area contacts

• Area owners (area-VM-meta-mono): @steveisok, @vitek-karas

A fix will likely require identifying the Regression_ro_2 method/instruction that carries a non-imm32 immediate and teaching the Mono AMD64 AOT emitter to materialize it correctly instead of asserting.

Structured data:

{
  "artifact_kind": "handoff",
  "linked_kbe": 134301,
  "workflow_artifact": "ci-fix"
}

Generated by CI Outer-Loop Failure Fixer · gpt56 · 55.5 AIC · ⌖ 14.5 AIC · ⊞ 26.9K · ◷