[tools] Add a tool to launch processes disclaming responsibility.

TODO: improve description.

Author: rolfbjarne

tests/xharness/Harness.cs

@@ -194,6 +194,29 @@ string GetVariable (string variable, string @default = null)
 			return result;
 		}
 
+#nullable enable
+		string? spawnerPath;
+		public string SpawnerPath {
+			get {
+                if (spawnerPath is null)
+					spawnerPath = Path.GetFullPath (Path.Combine (RootDirectory, "..", "tools", "spawner", "spawner"));
+				return spawnerPath;
+            }
+		}
+
+		public void UseSpawner (ProcessStartInfo processStartInfo, IList<string> arguments)
+		{
+			if (!string.IsNullOrEmpty (processStartInfo.Arguments))
+				throw new InvalidOperationException ($"ProcessStartInfo.Arguments must be empty when using UseSpawner.");
+
+			var originalFileName = processStartInfo.FileName;
+			processStartInfo.FileName = SpawnerPath;
+			processStartInfo.ArgumentList.Add (originalFileName);
+			foreach (var args in arguments)
+				processStartInfo.ArgumentList.Add (args);
+		}
+#nullable disable
+
 		public List<TestProject> TestProjects { get; } = new ();
 
 		readonly bool useSystemXamarinIOSMac; // if the system XI/XM should be used, or the locally build XI/XM.

tests/xharness/IHarness.cs

@@ -46,6 +46,8 @@ public interface IHarness {
 		bool InCI { get; }
 		bool UseTcpTunnel { get; }
 		string VSDropsUri { get; }
+		string SpawnerPath { get; }
+		void UseSpawner (System.Diagnostics.ProcessStartInfo startInfo, IList<string> arguments);
 
 		#endregion
 

tests/xharness/Jenkins/TestTasks/MacExecuteTask.cs

@@ -85,7 +85,10 @@ public override async Task RunTestAsync ()
 						proc.StartInfo.EnvironmentVariables ["DISABLE_SYSTEM_PERMISSION_TESTS"] = "1";
 					proc.StartInfo.EnvironmentVariables ["MONO_DEBUG"] = "no-gdb-backtrace";
 					proc.StartInfo.EnvironmentVariables.Remove ("DYLD_FALLBACK_LIBRARY_PATH"); // VSMac might set this, and the test may end up crashing
-					proc.StartInfo.Arguments = StringUtils.FormatArguments (arguments);
+
+					// Use the spawner to launch the app, to avoid issues with macOS getting confused who's the responsible process
+					Harness.UseSpawner (proc.StartInfo, arguments);
+
 					Jenkins.MainLog.WriteLine ("Executing {0} ({1})", TestName, Mode);
 					var log = Logs.Create ($"execute-{Platform}-{Timestamp}.txt", LogType.ExecutionLog.ToString ());
 					ICrashSnapshotReporter snapshot = null;

tools/Makefile

@@ -25,3 +25,4 @@ endif
 SUBDIRS+=mlaunch
 
 SUBDIRS += dotnet-linker
+SUBDIRS += spawner

tools/spawner/.gitignore

@@ -0,0 +1,3 @@
+.libs
+spawner
+

tools/spawner/Makefile

@@ -0,0 +1,15 @@
+TOP=../..
+include $(TOP)/Make.config
+include $(TOP)/mk/rules.mk
+
+.libs/osx-arm64/spawner: .libs/osx-arm64/spawner.o
+	$(Q_CCLD) $(CLANG) -arch $(DOTNET_osx-arm64_ARCHITECTURES) $< -o$@ -isysroot $(macos_SDK)
+
+.libs/osx-x64/spawner: .libs/osx-x64/spawner.o
+	$(Q_CCLD) $(CLANG) -arch $(DOTNET_osx-x64_ARCHITECTURES) $< -o$@ -isysroot $(macos_SDK)
+
+spawner: .libs/osx-arm64/spawner .libs/osx-x64/spawner
+	$(Q_LIPO) $(LIPO) $^ -create -output $@
+	$(Q) chmod +x $@
+
+all-local:: spawner

tools/spawner/README.md

@@ -0,0 +1,69 @@
+SPAWNER
+=======
+
+This is a very simple tool, which executes another process, disclaiming any
+responsibility for it.
+
+This is important when executing tests apps, because when macOS sees that an
+app uses API that needs specific entries in the Info.plist (such as the
+`NSAppleMusicUsageDescription`), the responsible process is where macOS looks
+for said key.
+
+Example crash report:
+
+```
+Process:               introspection [85822]
+Path:                  /Users/USER/*/introspection.app/Contents/MacOS/introspection
+Identifier:            com.xamarin.introspection
+Version:               1.0 (1.0)
+Code Type:             ARM-64 (Native)
+Parent Process:        dotnet [81129]
+Responsible:           Electron [68966]
+User ID:               501
+
+Date/Time:             2025-11-13 17:33:10.8123 +0100
+OS Version:            macOS 15.7.2 (24G325)
+Report Version:        12
+Anonymous UUID:        F22C0F06-0F16-E475-C0CB-264A0FF4F6A3
+
+
+Time Awake Since Boot: 27000 seconds
+
+System Integrity Protection: enabled
+
+Crashed Thread:        16  Dispatch queue: com.apple.root.default-qos
+
+Exception Type:        EXC_CRASH (SIGKILL)
+Exception Codes:       0x0000000000000000, 0x0000000000000000
+
+Termination Reason:    Namespace TCC, Code 0 
+This app has crashed because it attempted to access privacy-sensitive data without a usage description. The app's Info.plist must contain an NSAppleMusicUsageDescription key with a string value explaining to the user how the app uses this data.
+```
+
+The app crashed because macOS says it needs the `NSAppleMusicUsageDescription` entry in its `Info.plist` file.
+
+This is confusing, because introspection has an `NSAppleMusicUsageDescription` entry in its `Info.plist` file.
+
+Here's what happens:
+
+Note that there's a "Responsible [Process]" (Electron 68966) line, which is not the same as "Process" (introspection 85822), and this is the crux of the matter.
+
+In this particular case:
+
+* I opened the xharness project in VSCode.
+* I launched the xharness project in the debugger, and then ran introspection for Mac Catalyst.
+* The responsible process ended up being VS Code (aka Electron, with pid 85822), and that's where macOS ended up looking for the `NSAppleMusicUsageDescription` key.
+
+The fix is to launch `introspection` (and any other test app on macOS) using
+this `spawner` tool, which disclaims reponsibility for anything it launches,
+thus letting `introspection` be a grown up process and fully responsible for
+itself.
+
+Usage is simple: just pass the executable + any arguments to `spawner`.
+
+References:
+
+* https://gitlab.com/gnachman/iterm2/-/issues/10360
+* https://github.com/llvm/llvm-project/commit/041c7b84a4b925476d1e21ed302786033bb6035f#diff-a38ae411ccf0c85f3d7c0c45d8e1ad035030d5171d59e478b86a094941d3209dR16-R17
+* https://lldb.llvm.org/cpp_reference/PosixSpawnResponsible_8h_source.html
+* https://steipete.me/posts/2025/applescript-cli-macos-complete-guide

tools/spawner/spawner.c

@@ -0,0 +1,71 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT License.
+
+#include <dispatch/dispatch.h>
+#include <dlfcn.h>
+#include <signal.h>
+#include <spawn.h>
+#include <stdio.h>
+
+errno_t responsibility_spawnattrs_setdisclaim (posix_spawnattr_t *attrs, bool disclaim);
+
+int main (int argc, char** argv, char** envp)
+{
+	if (argc < 2) {
+		fprintf (stderr,
+			"spawner: launch a subprocess, disclaiming all responsibilities with regards to TCC:\n"
+			"usage: spawner <command> [arguments]\n");
+		return 1;
+	}
+
+	int rv;
+	// Behave as exec
+	short flags = POSIX_SPAWN_SETEXEC;
+	posix_spawnattr_t spawnattr;
+	sigset_t sigset;
+
+	rv = posix_spawnattr_init (&spawnattr);
+	if (rv) {
+		fprintf (stderr, "Failed to execute 'posix_spawnattr_init': %i (%s)\n", rv, strerror (rv));
+		return 1;
+	}
+
+	// Reset the signal mask
+	sigemptyset (&sigset);
+	rv = posix_spawnattr_setsigmask (&spawnattr, &sigset);
+	if (rv) {
+		fprintf (stderr, "Failed to execute 'posix_spawnattr_setsigmask': %i (%s)\n", rv, strerror (rv));
+		return 1;
+	}
+	flags |= POSIX_SPAWN_SETSIGMASK;
+
+	// Reset all signals to their default handlers
+	sigfillset (&sigset);
+	rv = posix_spawnattr_setsigdefault (&spawnattr, &sigset);
+	if (rv) {
+		fprintf (stderr, "Failed to execute 'posix_spawnattr_setsigdefault': %i (%s)\n", rv, strerror (rv));
+		return 1;
+	}
+	flags |= POSIX_SPAWN_SETSIGDEF;
+
+	rv = posix_spawnattr_setflags (&spawnattr, flags);
+	if (rv) {
+		fprintf (stderr, "Failed to execute 'posix_spawnattr_setflags': %i (%s)\n", rv, strerror (rv));
+		return 1;
+	}
+
+	rv = responsibility_spawnattrs_setdisclaim (&spawnattr, 1);
+	if (rv) {
+		fprintf (stderr, "Failed to execute 'responsibility_spawnattrs_setdisclaim': %i (%s)\n", rv, strerror (rv));
+		return 1;
+	}
+
+	pid_t pid = 0;
+	rv = posix_spawnp (&pid, argv [1], NULL, &spawnattr, argv + 1, envp);
+	posix_spawnattr_destroy (&spawnattr);
+
+	// posix_spawnp shouldn't return (because we set the POSIX_SPAWN_SETEXEC flag)
+	// so if it did, something went wrong
+	fprintf (stderr, "Failed to execute '%s': %i (%s)\n", argv [1], rv, strerror (rv));
+	return 1;
+}