[gtk+/gdk-egl-x11: 1/4] gdk/x11: Resolve glXQueryVersion manually

[Emmanuele Bassi <ebassi src gnome org>]

commit e246a81bc3aed8f48d6659d644212884878876f7
Author: Emmanuele Bassi <ebassi gnome org>
Date:   Tue Nov 29 00:03:54 2016 +0000

    gdk/x11: Resolve glXQueryVersion manually
    
    Instead of going through libepoxy, which may have unintended side
    effects, we should ask the X11 server if it supports the GLX extension
    in the good old way, by dlsym() (or g_module_symbol()). This should
    avoid crashes in case the X server is "special".

 gdk/x11/gdkglcontext-x11.c |   25 +++++++++++++++++++++++--
 1 files changed, 23 insertions(+), 2 deletions(-)
---
diff --git a/gdk/x11/gdkglcontext-x11.c b/gdk/x11/gdkglcontext-x11.c
index 0819f89..274390f 100644
--- a/gdk/x11/gdkglcontext-x11.c
+++ b/gdk/x11/gdkglcontext-x11.c
@@ -847,6 +847,9 @@ gdk_x11_screen_init_gl (GdkScreen *screen)
   Display *dpy;
   int error_base, event_base;
   int screen_num;
+  GModule *module;
+  typedef Bool (* FP_GLX_Query_Version) (Display *dpy, int *major, int *minor);
+  FP_GLX_Query_Version glx_query_version;
 
   if (display_x11->have_glx)
     return TRUE;
@@ -856,8 +859,26 @@ gdk_x11_screen_init_gl (GdkScreen *screen)
 
   dpy = gdk_x11_display_get_xdisplay (display);
 
-  if (!glXQueryExtension (dpy, &error_base, &event_base))
-    return FALSE;
+  /* We do this without going through libepoxy to avoid the trampoline and
+   * ensure that we don't have side effects that may cause crashes due to
+   * server that lie, or that simply do not support GLX.
+   *
+   * See: https://bugzilla.gnome.org/show_bug.cgi?id=775279
+   */
+  module = g_module_open (NULL, 0);
+  if (!g_module_symbol (module, "glXQueryVersion", (gpointer) &glx_query_version))
+    {
+      g_module_close (module);
+      return FALSE;
+    }
+
+  if (!(* glx_query_version) (dpy, &error_base, &event_base))
+    {
+      g_module_close (module);
+      return FALSE;
+    }
+
+  g_module_close (module);
 
   screen_num = GDK_X11_SCREEN (screen)->screen_num;