[iOS] mlaunch fails to launch apps on simulator with Xcode 26.4 — simctl SIGKILL'd during orchestration

[PureWeen]

Description

CoreCLR MAUI template app fails to launch on iOS simulator with APP_LAUNCH_FAILURE (XHarness exit code 83). The app builds successfully but is immediately SIGKILL'd (signal 9) on simulator launch. Mono runtime apps launch fine on the same simulator.

Root Cause

The simulator watchdog handling differs between CoreCLR and Mono apps. For the CoreCLR test, `Xamarin.Hosting` reports "Simulator watchdogs are not disabled" and shuts down/reboots the simulator before launching. After reboot, the simulator goes to `Shutdown` state and the launch fails. For Mono apps, watchdogs are already disabled and the app launches directly without a reboot cycle.

Crash Sequence (from XHarness logs)

```
Xamarin.Hosting: Simulator watchdogs are not disabled for 'iPhone 11 Pro (iOS 18.5)'
Xamarin.Hosting: Shutting down simulator...
xcrun simctl shutdown 94004A3B-...
Xamarin.Hosting: Successfully disabled simulator watchdogs
Xamarin.Hosting: Launching simulator application
Xamarin.Hosting: Ready notification received
Xamarin.Hosting: Launching on iPhone 11 Pro (iOS 18.5) by executing:
xcrun simctl launch --console --terminate-running-process ... com.companyname.teste6b06bb...

An error was encountered processing the command (domain=com.apple.CoreSimulator.SimError, code=405):
Unable to lookup in current state: Shutdown
error HE0042: Could not launch the app ... simctl returned exit code 149
```

Device Log (filtered by app)

```
getpwuid_r did not find a match for uid 501
Filtering the log data using "senderImagePath CONTAINS "Teste6b06bb801976599085""
Child process terminated with signal 9: Killed
Process 4759 already exited or busy: No process is associated with this object.
Killing process 4759 as it was cancelled
```

The app never produces any output — killed immediately at launch. No crash report or stack trace.

Comparison: Passing Mono Test vs Failing CoreCLR Test

	Mono (Test8951 - passes)	CoreCLR (Teste6b06bb - fails)
Watchdogs	"already disabled"	"not disabled" → shutdown/reboot
Simulator state	Stays booted	Goes to Shutdown
App launch	Gets PID, runs normally	SIGKILL'd (signal 9) immediately
simctl exit	0	137 (SIGKILL) then 149 (Shutdown)

Environment

• Xcode 26.4
• iOS Simulator: iPhone 11 Pro (iOS 18.5)
• SDK: 11.0.100-preview.4.26224.122
• XHarness: 11.0.0-prerelease.26107.1
• Build config: Release, CoreCLR (`-p:UseMonoRuntime=false`)
• Test: `AppleTemplateTests.RunOniOS_MauiRelease_CoreCLR`

Build Reference

PR dotnet/maui#35171, Build 1402884 — `RunOniOS_MauiRelease ARM64` job

Attached Logs

See attached XHarness logs from the failing test run.

[PureWeen]

XHarness Log Files

Teste6b06bb801976599085.log (simulator device log — filtered by app)

getpwuid_r did not find a match for uid 501
Filtering the log data using "senderImagePath CONTAINS "Teste6b06bb801976599085""
Child process terminated with signal 9: Killed
Process 4759 already exited or busy: No process is associated with this object.
Killing process 4759 as it was cancelled

com.companyname.teste6b06bb801976599085.log (mlaunch/Xamarin.Hosting log)

[17:36:06.5648170] Using Xcode 26.4 found in /Applications/Xcode_26.4.app
[17:36:06.8534850] Xamarin.Hosting: Simulator watchdogs are not disabled for 'iPhone 11 Pro (iOS 18.5)'
[17:36:06.8535190] Xamarin.Hosting: Shutting down simulator...
[17:36:06.8541980] xcrun simctl shutdown 94004A3B-1014-405A-A097-17B73A630212
[17:36:10.0554790] Xamarin.Hosting: Successfully disabled simulator watchdogs
[17:36:10.0631490] Xamarin.Hosting: Launching simulator application 'com.apple.iphonesimulator'
[17:36:10.8969860] Xamarin.Hosting: Ready notification received from the simulator.
[17:36:10.9080480] Xamarin.Hosting: Launching on iPhone 11 Pro (iOS 18.5) by executing:
    xcrun simctl launch --console --terminate-running-process 94004A3B com.companyname.teste6b06bb801976599085
[17:36:11.0760620] An error was encountered (domain=com.apple.CoreSimulator.SimError, code=405):
[17:36:11.0761060] Unable to lookup in current state: Shutdown
[17:36:11.2436600] error HE0042: Could not launch the app: simctl returned exit code 149
[17:36:11.2703620]    at Xamarin.Hosting.Services.LaunchApplicationInSimulatorInternalAsyncSimCtl
[17:36:11.2704120]    at Xamarin.Hosting.Services.LaunchApplicationInSimulatorAsync
[17:36:11.2704220]    at Xamarin.Launcher.SimController.LaunchAsync
[17:36:11.2704270]    at Xamarin.Launcher.Driver.LaunchSimulatorAsync

run-ios-simulator-64_18.5.log (XHarness run log)

[17:36:06.2887810] System log: /Users/cloudtest/Library/Logs/CoreSimulator/94004A3B-.../system.log
[17:36:06.2925530] Launching the app
[17:36:07.3000920] Process simctl exited with 137
[17:36:11.2728550] Process mlaunch exited with 1
[17:36:11.4767150] An error (domain=com.apple.CoreSimulator.SimError, code=405):
[17:36:11.4767910] Unable to lookup in current state: Shutdown
[17:36:11.4780540] Process simctl exited with 149

[rolfbjarne]

Is there a binlog for the app that crashes?

[kotlarmilos]

The binlog shows a successful CoreCLR build with the .app successfully installed on the simulator. This looks like Xcode 26.4 + iOS 18.5 problem. The problem is that Xamarin.Hosting assumes the simulator is booted after its watchdog-disable shutdown/restart cycle, but on Xcode 26.4 + iOS 18.5 the CoreSimulator device is actually still in Shutdown state when xcrun simctl launch is invoked, which fails with "unable to lookup in current state: Shutdown".

The Mono RunOniOS_MauiRelease ARM64 leg in the same build failed identically.

issue-35261-logs.zip

[PureWeen]

Update: Reproduced locally — NOT CoreCLR specific, it's mlaunch + Xcode 26.4

Key Finding

This is not a CoreCLR issue. Both Mono and CoreCLR apps fail identically when launched via mlaunch/XHarness on Xcode 26.4.1. Direct simctl launch works fine — the bug is specifically in mlaunch's interaction with the simulator under Xcode 26.4.

Local Reproduction (Xcode 26.4.1, macOS 26.4.1)

Direct simctl launch — WORKS:

$ xcrun simctl launch --console --terminate-running-process <device> com.microsoft.maui.sandbox
com.microsoft.maui.sandbox: 30919   ← app gets PID, launches fine

XHarness/mlaunch launch — FAILS (CoreCLR):

$ dotnet xharness apple run --app=Sandbox.app --target=ios-simulator-64_18.5 --timeout=00:00:30
Process simctl exited with 137   ← SIGKILL
Process mlaunch exited with 1
Unable to lookup in current state: Shutdown
XHarness exit code: 83 (APP_LAUNCH_FAILURE)

XHarness/mlaunch launch — FAILS (Mono too!):

$ dotnet xharness apple run --app=Sandbox.app --target=ios-simulator-64_18.5 --timeout=00:00:30
Process mlaunch exited with 137
Run timed out after 30 seconds
XHarness exit code: 90 (APP_LAUNCH_TIMEOUT)

Why CI Mono tests "passed" but CoreCLR failed

On CI, tests run sequentially. The Mono test (RunOniOS_MauiRelease) likely ran on a simulator where watchdogs were already disabled from a previous test. The CoreCLR test (RunOniOS_MauiRelease_CoreCLR) hit the simulator first — mlaunch tried to disable watchdogs, shut down the simulator, and the reboot cycle broke subsequent launches.

Updated diagnosis

• Bug location: mlaunch (xamarin-macios) — broken simulator management under Xcode 26.4
• NOT affected: CoreCLR runtime, MAUI framework code, app building
• Workaround: Direct simctl launch works; only mlaunch's orchestration is broken
• Xcode 26.3: Works fine with mlaunch (tested locally before Xcode 26.4 install)

Title update suggestion

Change from "[iOS] CoreCLR template app SIGKILL'd on simulator launch" to "[iOS] mlaunch fails to launch apps on simulator with Xcode 26.4 — simctl SIGKILL'd during orchestration"

[rolfbjarne]

Turns out I've already fixed this: https://devdiv@dev.azure.com/devdiv/DevDiv/_git/macios-mlaunch/commit/4ba65e5f085ed2dfc22868c69e4e5bd8c0b14e7a

[rolfbjarne]

mlaunch bump in xharness: dotnet/xharness#1591

[rolfbjarne]

This is the final fix, the xharness bump in dotnet/maui: dotnet/maui#35292