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Bug 2154

Summary: X11: Crash in ' SDL_ShowSimpleMessageBox()' since commit d4a39491577f
Product: SDL Reporter: Jonas Kulla <ancurio_bugzilla>
Component: videoAssignee: Sam Lantinga <slouken>
Status: RESOLVED FIXED QA Contact: Sam Lantinga <slouken>
Severity: major    
Priority: P2    
Version: HG 2.1   
Hardware: x86_64   
OS: Linux   
Attachments: Quick n ugly fix

Description Jonas Kulla 2013-10-14 20:43:53 UTC 
After commit d4a39491577f (https://hg.libsdl.org/SDL/rev/d4a39491577f), SDL crashes in 'SDL_ShowSimpleMessageBox()' for me (segmentation fault).

I have narrowed the problem down to (video/x11/SDL_x11messagebox.c:373):

    if ( messageboxdata->window ) {
        SDL_DisplayData *displaydata =
            (SDL_DisplayData *) SDL_GetDisplayForWindow(messageboxdata->window)->driverdata;
        windowdata = (SDL_WindowData *)messageboxdata->window->driverdata;
        data->screen = displaydata->screen;
    } else {
        data->screen = DefaultScreen( display );
    }

where SDL_GetDisplayForWindow (video/SDL_video.c:996):

    int displayIndex = SDL_GetWindowDisplayIndex(window);
    if (displayIndex >= 0) {
        return &_this->displays[displayIndex];
    } else {
        return NULL;
    }

'SDL_GetWindowDisplayIndex()' returns -1, making 'SDL_GetDisplayForWindow()' return NULL, while the first code snippet dereferences this NULL pointer (messageboxdata->window) and causes the segfault.

Anything else I can do to help find the problem?
Comment 1 Jonas Kulla 2013-10-14 20:46:20 UTC 
Sorry, I meant to write the NULL pointer is dereferenced via "->driverdata".
Comment 2 Jonas Kulla 2013-10-14 21:03:14 UTC 
Upon further investigation, there's something about this code calling the device vfunc (SDL_video.c:3141):

    if (_this && _this->ShowMessageBox) {
        retval = _this->ShowMessageBox(_this, messageboxdata, buttonid);
    }

The dereferenced function I see being called in my debugger is (SDL_x11messagebox.c:700):

int
X11_ShowMessageBox(const SDL_MessageBoxData *messageboxdata, int *buttonid)


Which on first sight looks like we're calling with the wrong signature. Could this be the problem?
Comment 3 Jonas Kulla 2013-10-14 21:23:41 UTC 
Created attachment 1367 [details]
Quick n ugly fix
Comment 4 Sam Lantinga 2013-10-15 02:00:05 UTC 
I actually fixed this earlier today, thanks for the report!
http://hg.libsdl.org/SDL/rev/a31914a35076
Comment 5 Jonas Kulla 2013-10-15 02:53:45 UTC 
Oh, what a coincidence =) Thanks!