[runtime] Handle fatal managed exceptions a bit better in the runtime. (

#15029)

Handle managed exceptions a bit better when we know there won't be any other
managed frames further up the stack (such as in the main method). In this
case, there's no use in trying to convert the managed exception into an
Objective-C exception, because we already know the process will be terminated.

Instead just print the exception to stderr, and abort immediately.

This means we'll actually get some useful information printed to stderr.

runtime/monotouch-main.m

@@ -443,26 +443,22 @@ - (void) memoryWarning: (NSNotification *) sender
 
 	if (xamarin_executable_name) {
 		assembly = xamarin_open_and_register (xamarin_executable_name, &exception_gchandle);
-		if (exception_gchandle != NULL)
-			xamarin_process_managed_exception_gchandle (exception_gchandle);
+		xamarin_process_fatal_exception_gchandle (exception_gchandle, "An exception occurred while opening the main executable");
 	} else {
 		const char *last_slash = strrchr (argv [0], '/');
 		const char *basename = last_slash ? last_slash + 1 : argv [0];
 		char *aname = xamarin_strdup_printf ("%s.exe", basename);
 
 		assembly = xamarin_open_and_register (aname, &exception_gchandle);
 		xamarin_free (aname);
-
-		if (exception_gchandle != NULL)
-			xamarin_process_managed_exception_gchandle (exception_gchandle);
+		xamarin_process_fatal_exception_gchandle (exception_gchandle, "An exception occurred while opening an assembly");
 	}
 
 	if (xamarin_supports_dynamic_registration) {
 		MonoReflectionAssembly *rassembly = mono_assembly_get_object (mono_domain_get (), assembly);
 		xamarin_register_entry_assembly (rassembly, &exception_gchandle);
 		xamarin_mono_object_release (&rassembly);
-		if (exception_gchandle != NULL)
-			xamarin_process_managed_exception_gchandle (exception_gchandle);
+		xamarin_process_fatal_exception_gchandle (exception_gchandle, "An exception occurred while opening the entry assembly");
 	}
 
 	DEBUG_LAUNCH_TIME_PRINT ("\tAssembly register time");

runtime/runtime.m

@@ -1087,6 +1087,17 @@ -(void) xamarinSetFlags: (enum XamarinGCHandleFlags) flags;
 	xamarin_process_managed_exception_gchandle (gchandle);
 }
 
+void
+xamarin_process_fatal_exception_gchandle (GCHandle gchandle, const char *message)
+{
+	if (gchandle == INVALID_GCHANDLE)
+		return;
+
+	NSString *fatal_message = [NSString stringWithFormat:@"%s\n%@", message, xamarin_print_all_exceptions (gchandle)];
+	NSLog (@PRODUCT ": %@", fatal_message);
+	xamarin_assertion_message ([fatal_message UTF8String]);
+}
+
 // Because this function won't always return, it will take ownership of the GCHandle and free it.
 void
 xamarin_process_managed_exception_gchandle (GCHandle gchandle)
@@ -1136,7 +1147,7 @@ -(void) xamarinSetFlags: (enum XamarinGCHandleFlags) flags;
 	while (xamarin_gc_pump) {
 		GCHandle exception_gchandle = INVALID_GCHANDLE;
 		xamarin_gc_collect (&exception_gchandle);
-		xamarin_process_managed_exception_gchandle (exception_gchandle);
+		xamarin_process_fatal_exception_gchandle (exception_gchandle, "An exception occurred while running the GC in a loop");
 		MONO_ENTER_GC_SAFE;
 		usleep (1000000);
 		MONO_EXIT_GC_SAFE;
@@ -1300,16 +1311,10 @@ -(void) xamarinSetFlags: (enum XamarinGCHandleFlags) flags;
 #endif // defined(CORECLR_RUNTIME)
 
 	xamarin_bridge_call_runtime_initialize (&options, &exception_gchandle);
-	if (exception_gchandle != INVALID_GCHANDLE) {
-		NSLog (@PRODUCT ": An exception occurred when calling Runtime.Initialize:\n%@", xamarin_print_all_exceptions (exception_gchandle));
-		xamarin_assertion_message ("Can't continue if Runtime.Initialize fails.");
-	}
+	xamarin_process_fatal_exception_gchandle (exception_gchandle, "An exception occurred while calling Runtime.Initialize");
 
 	xamarin_bridge_register_product_assembly (&exception_gchandle);
-	if (exception_gchandle != INVALID_GCHANDLE) {
-		NSLog (@PRODUCT ": An exception occurred when registering the product assembly:\n%@", xamarin_print_all_exceptions (exception_gchandle));
-		xamarin_assertion_message ("Can't continue if registering the product assembly fails.");
-	}
+	xamarin_process_fatal_exception_gchandle (exception_gchandle, "An exception occurred while registering the product assembly");
 
 #if !defined (CORECLR_RUNTIME)
 	xamarin_install_mono_profiler (); // must be called before xamarin_install_nsautoreleasepool_hooks or xamarin_enable_new_refcount

runtime/xamarin/runtime.h

@@ -253,6 +253,7 @@ void			xamarin_process_nsexception (NSException *exc);
 void			xamarin_process_nsexception_using_mode (NSException *ns_exception, bool throwManagedAsDefault, GCHandle *output_exception);
 void			xamarin_process_managed_exception (MonoObject *exc);
 void			xamarin_process_managed_exception_gchandle (GCHandle gchandle);
+void			xamarin_process_fatal_exception_gchandle (GCHandle gchandle, const char *message);
 void			xamarin_throw_product_exception (int code, const char *message);
 GCHandle		xamarin_create_product_exception (int code, const char *message);
 GCHandle		xamarin_create_product_exception_with_inner_exception (int code, GCHandle inner_exception_gchandle /* will be freed */, const char *message);