Bug 59798 - mtouch crashes when passed any gcc_flags parameter
Summary: mtouch crashes when passed any gcc_flags parameter
Alias: None
Product: iOS
Classification: Xamarin
Component: Tools ()
Version: XI 11.0 (xcode9)
Hardware: Macintosh Mac OS
: --- major
Target Milestone: 15.5
Assignee: Rolf Bjarne Kvinge [MSFT]
Depends on:
Reported: 2017-09-27 19:09 UTC by Ethan Lee
Modified: 2017-11-20 10:19 UTC (History)
3 users (show)

Is this bug a regression?: ---
Last known good build:

msbuild output, Debug iPhoneSimulator (18.68 KB, text/plain)
2017-09-27 19:09 UTC, Ethan Lee

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Description Ethan Lee 2017-09-27 19:09:07 UTC
Created attachment 24965 [details]
msbuild output, Debug iPhoneSimulator

When building with Visual Studio for Mac (version 7.1.5 build 2), mtouch will crash when attempting to pass gcc_flags of any kind (for example, when linking against libSDL2.a). Attached is the full msbuild output, including the crash trace.

iOSTest was based on the single-screen template, with all of the code removed in favor of a basic Main() function, calling SDL_Init and SDL_Quit via SDL2# (which is bundled in with the project):


libSDL2.a was built with SDL's provided build script, and supports i386/x86_64/armv7/armv7s/arm64.

The problem appears to be here, where it fails to find a matching name and proceeds to hit a NullReference:


When no gcc_flags are passed (including gcc_flags ""), the build succeeds and throws an Exception at runtime when it can't find the SDL_Init entry point, as it should.

The gcc_flags input was based on the Xamarin.iOS documentation, which does appear to be out of date given that it calls the text box "Extra" as opposed to "Additional mtouch arguments," which is what it's called in the latest version of VSM:

Comment 1 Rolf Bjarne Kvinge [MSFT] 2017-09-28 10:15:39 UTC
(In reply to Ethan Lee from comment #0)

> iOSTest was based on the single-screen template, with all of the code
> removed in favor of a basic Main() function, calling SDL_Init and SDL_Quit
> via SDL2# (which is bundled in with the project):

If you remove all the code except for a Main function, the main executable won't have a reference to Xamarin.iOS.dll, and that's the reason for the NullReferenceException.

Using any API from Xamarin.iOS.dll will work around this (it can be as simple as "Console.WriteLine (typeof (UIKit.UIWindow));" for instance).

In any case I've added detection for this in our tools, so that we show a proper error instead of an MT0000: https://github.com/xamarin/xamarin-macios/pull/2801
Comment 2 Rolf Bjarne Kvinge [MSFT] 2017-09-28 15:38:24 UTC
Fixed (to show a better error): https://github.com/xamarin/xamarin-macios/commit/eeb62568342c466bb6cb91f9a5cb22e1c4be3f9a
Comment 3 Mohak Barokar 2017-11-20 09:58:55 UTC

Can you please confirm the reproduction steps of this issue?

I have tried with following reproduction steps:
1. Create iOS single view Application 
2. Pass any gcc flag arguments in  "Additional mtouch arguments" such as "--gcc_flags="-framework AVFoundation -framework CoreMedia""
3. Build solution

Following is the build config this is verified on:
Comment 4 Rolf Bjarne Kvinge [MSFT] 2017-11-20 10:01:24 UTC

The gcc flags is a red herring in this case, to repro the NullReferenceException:

1. Create iOS Single view application.
2. Remove all code, except a single, empty Main function:

    class MyApp {
        static void Main () {}
3. Build solution.
Comment 5 Mohak Barokar 2017-11-20 10:19:37 UTC
This bug is verified on following d15_5 config according to Comment #4 :

 -Visual Studio Professional 2017 for Mac (Preview) Version 7.4 Preview (7.4 build 632)
 -Mono (2017-10/2cc0f9029ae) (64-bit)
 -Xamarin.Android Version:
 -Xamarin.Mac Version:
 -Xamarin.iOS Version:

 Detailed Build Config: https://gist.github.com/raghorteprasad/2a6a24dc25d226b4012ddddb1975a152

 Screencast Link: http://www.screencast.com/t/75bYCKcl9YwM

The issue is fixed and marking it as Verified Fixed.