Prevent AV in processinfo2 while suspended (#55379)

Author: John Salem

src/coreclr/vm/eventing/eventpipe/ep-rt-coreclr.h

@@ -1169,7 +1169,22 @@ ep_rt_entrypoint_assembly_name_get_utf8 (void)
 {
 	STATIC_CONTRACT_NOTHROW;
 
-	return reinterpret_cast<const ep_char8_t*>(GetAppDomain ()->GetRootAssembly ()->GetSimpleName ());
+	AppDomain *app_domain_ref = nullptr;
+	Assembly *assembly_ref = nullptr;
+
+	app_domain_ref = GetAppDomain ();
+	if (app_domain_ref != nullptr)
+	{
+		assembly_ref = app_domain_ref->GetRootAssembly ();
+		if (assembly_ref != nullptr)
+		{
+			return reinterpret_cast<const ep_char8_t*>(assembly_ref->GetSimpleName ());
+		}
+	}
+
+	// fallback to the empty string if we can't get assembly info, e.g., if the runtime is
+	// suspended before an assembly is loaded.
+	return reinterpret_cast<const ep_char8_t*>("");
 }
 
 static

src/tests/tracing/eventpipe/diagnosticport/diagnosticport.cs

@@ -388,6 +388,42 @@ public static async Task<bool> TEST_ConfigValidation()
             return fSuccess;
         }
 
+        public static async Task<bool> TEST_CanGetProcessInfo2WhileSuspended()
+        {
+            bool fSuccess = true;
+            Task<bool> subprocessTask = Utils.RunSubprocess(
+                currentAssembly: Assembly.GetExecutingAssembly(),
+                environment: new Dictionary<string,string> 
+                {
+                    { Utils.DiagnosticPortSuspend, "1" }
+                },
+                duringExecution: (int pid) =>
+                {
+                    Stream stream = ConnectionHelper.GetStandardTransport(pid);
+
+                    // 0x04 = ProcessCommandSet, 0x04 = ProcessInfo2
+                    var processInfoMessage = new IpcMessage(0x04, 0x04);
+                    Logger.logger.Log($"Wrote: {processInfoMessage}");
+                    IpcMessage response = IpcClient.SendMessage(stream, processInfoMessage);
+                    Logger.logger.Log($"Received: [{response.Payload.Select(b => b.ToString("X2") + " ").Aggregate(string.Concat)}]");
+                    ProcessInfo2 processInfo2 = ProcessInfo2.TryParse(response.Payload);
+                    Utils.Assert(String.IsNullOrEmpty(processInfo2.ManagedEntrypointAssemblyName));
+
+                    // send resume command on this connection
+                    var message = new IpcMessage(0x04,0x01);
+                    Logger.logger.Log($"Sent: {message.ToString()}");
+                    response = IpcClient.SendMessage(ConnectionHelper.GetStandardTransport(pid), message);
+                    Logger.logger.Log($"Received: {response.ToString()}");
+
+                    return Task.FromResult(true);
+                }
+            );
+
+            fSuccess &= await subprocessTask;
+
+            return fSuccess;
+        }
+
         public static async Task<int> Main(string[] args)
         {
             if (args.Length >= 1)