Ad-hoc re-sign bootstrap dotnet on macOS to prevent SIGKILL

[jankratochvilcz]

Problem

I found this because on my Mac some unit tests are failing, namely RoslynCodeTaskFactory_Tests.

On macOS, the bootstrap dotnet binary at artifacts/bin/bootstrap/core/dotnet is frequently killed by Gatekeeper with SIGKILL (exit code 137) immediately upon execution. This happens because the dotnet-install.sh script downloads and copies the apphost binary into the bootstrap directory, and macOS code-signing enforcement rejects it in its new location.

This causes any test that invokes the bootstrap dotnet to fail — most visibly tests using RoslynCodeTaskFactory, which shells out to dotnet csc.dll to compile inline tasks. The failure manifests as:

• MSB6006: "csc.exe" exited with code 137
• Killed: 9 when running the bootstrap dotnet directly

The error is confusing because exit code 137 typically suggests OOM, but the real cause is macOS security policy.

Solution

Add an Exec step at the end of the BootstrapNetCore target in eng/BootStrapMsBuild.targets that ad-hoc re-signs the bootstrap dotnet binary on macOS:

<Exec Command="codesign --force --sign - \&quot;$(InstallDir)dotnet\&quot;"
      Condition="$([MSBuild]::IsOSPlatform('osx'))" />

This runs automatically as part of every bootstrap build, so macOS developers never need to manually troubleshoot this issue. The --force --sign - flags replace the existing signature with an ad-hoc local signature that macOS accepts. The condition ensures this only runs on macOS — Windows and Linux are unaffected.

Testing

1. Cleaned the repo (rm -rf artifacts/)
2. Ran ./build.sh -v quiet — build succeeded, codesign step ran automatically
3. Verified artifacts/bin/bootstrap/core/dotnet --version works (previously: Killed: 9)
4. Ran dotnet test src/Tasks.UnitTests/ --filter BothForceAndMultiThreadedWork — passed ✅

[Copilot]

Pull request overview

Adds a macOS-specific mitigation to the bootstrap build so the downloaded/copied bootstrap dotnet doesn’t get immediately terminated by Gatekeeper (SIGKILL / exit code 137), which otherwise breaks tests that shell out to the bootstrap dotnet (e.g., RoslynCodeTaskFactory scenarios).

Changes:

• Add a macOS-only codesign --force --sign - step at the end of the BootstrapNetCore target.
• Document the rationale inline in BootStrapMsBuild.targets to clarify the Gatekeeper/SIGKILL behavior.

[jankratochvilcz]

I'm not 100% sure how this is not failing the unit tests in CI for Mac, maybe it is configured more loosely 🤔

[github-actions]

Expert Review — 24-Dimension Analysis

PR #13513: Ad-hoc re-sign bootstrap dotnet on macOS to prevent SIGKILL

Clean, well-scoped fix for a real macOS developer pain point. All 24 review dimensions pass.

Summary Table

#	Dimension	Verdict	Notes
1	Backwards Compatibility	✅ LGTM	Build infra only; no user-facing change
2	ChangeWave Discipline	✅ LGTM	Not needed — no behavior change
3	Performance & Allocation Awareness	✅ LGTM	Single sub-second codesign call
4	Test Coverage & Completeness	✅ LGTM	Validated by bootstrap usage; manual testing documented
5	Error Message Quality	✅ LGTM	Exec propagates codesign errors naturally
6	Logging & Diagnostics	✅ LGTM	Exec task auto-logs to binlog
7	String Comparison Correctness	✅ N/A	No string comparisons
8	API Surface Discipline	✅ N/A	No API changes
9	Target Authoring Quality	✅ LGTM	Correctly placed after all Copy steps
10	Cross-Platform Correctness	✅ LGTM	IsOSPlatform('osx') correct; \ normalized to / on macOS; " handles spaces; Windows/Linux unaffected
11	Code Simplification	✅ LGTM	Minimal, clean 4-line addition
12	Concurrency Safety	✅ LGTM	Sequential within target; no shared state
13	Naming & Clarity	✅ LGTM	Comment explains why (Gatekeeper + exit code 137)
14	SDK Integration Boundary	✅ LGTM	Properly scoped to bootstrap infrastructure
15	Evaluation Model Integrity	✅ N/A	Not evaluation code
16	Correctness & Edge Cases	✅ LGTM	DependsOnTargets="AcquireSdk" guarantees binary exists; --force makes it idempotent; Exec fails build on error (correct)
17	Dependency Management	✅ LGTM	codesign is a macOS system binary; no new deps
18	Security & Trust	✅ LGTM	Ad-hoc signing is canonical for local dev; InstallDir is a local property not injectable externally; --force needed to replace the now-invalid original sig
19	Build Infrastructure Care	✅ LGTM	End-of-target placement correct; sub-second overhead; no CI regression
20	Documentation Accuracy	✅ LGTM	Inline comment is accurate and actionable
21	Binary Log Completeness	✅ LGTM	Exec task events captured automatically
22	Scope Discipline	✅ LGTM	Single concern, minimal diff, well-documented
23	Design Before Implementation	✅ LGTM	Ad-hoc re-signing is the standard macOS solution
24	Ecosystem Impact	✅ LGTM	Only affects local dev/test builds on macOS

Key Validations

• Path correctness: $(InstallDir) has trailing \ → MSBuild normalizes to / on macOS → codesign receives valid POSIX path with "..." quoting.
• Idempotency: --force allows repeated runs without error.
• Fail-fast: Exec defaults to IgnoreExitCode="false", so a codesign failure immediately surfaces rather than causing a confusing downstream SIGKILL.
• No regressions: Windows/Linux gated out by IsOSPlatform('osx'). The BootstrapFull target (Windows-only) is unaffected.

Verdict: APPROVE — All 24 dimensions clean. No blocking issues, no suggestions.

Generated by Expert Code Review (on open) for issue #13513 · ● 4.5M

[ViktorHofer]

Does codesign need sudo permissions?

[jankratochvilcz]

@ViktorHofer it doesn't, it should be designed to run as a regular user.

[JanProvaznik]

@jankratochvilcz please merge with squash next time