Fix crash in WGL context creation

GLContextWGL::Initialize() gets called before OpenGL extensions
get bound to the driver object, causing a nullptr dereference crash
when using OpenGL as the RHI backend.

This change modifies the GL bindings generation script to force
it to produce code that checks whether the problem function has been
bound already or not. The WGL context code that uses the function
already handles cases where it receives nullptr as return value, so
the initialization succeeds.

Fixes: QTBUG-124370
Change-Id: I53f885cd962ef7feb8c71b8a10c7d17684c43149
Reviewed-on: https://codereview.qt-project.org/c/qt/qtwebengine-chromium/+/554966
Reviewed-by: Allan Sandfeld Jensen <[email protected]>
Reviewed-on: https://codereview.qt-project.org/c/qt/qtwebengine-chromium/+/560809
Reviewed-by: Peter Varga <[email protected]>

Author: Kaloyan Chehlarski

chromium/ui/gl/generate_bindings.py

@@ -43,6 +43,8 @@
                 function.  This may happen for example when functions
                 are added to a new version of an extension, but the
                 extension string is not modified.
+   check_for_nullptr: Workaround for QTBUG-124370. Adds a check that ensures
+                the function has been bound already.
 By default, the function gets its name from the first name in its names or
 versions array. This can be overridden by supplying a 'known_as' key.
 
@@ -2980,7 +2982,8 @@
   'arguments': 'HDC hdc', },
 { 'return_type': 'HGLRC',
   'names': ['wglCreateContextAttribsARB'],
-  'arguments': 'HDC hDC, HGLRC hShareContext, const int* attribList', },
+  'arguments': 'HDC hDC, HGLRC hShareContext, const int* attribList',
+  'check_for_nullptr': True, },
 { 'return_type': 'HGLRC',
   'names': ['wglCreateLayerContext'],
   'arguments': 'HDC hdc, int iLayerPlane', },
@@ -3727,8 +3730,12 @@ def MakeArgNames(arguments):
       file.write('  driver_->fn.%sFn(%s);\n' %
           (function_name, argument_names))
     else:
-      file.write('  return driver_->fn.%sFn(%s);\n' %
-          (function_name, argument_names))
+      if ('check_for_nullptr' in func):
+        file.write('  return driver_->fn.%sFn ?\n driver_->fn.%sFn(%s)\n : nullptr;\n' %
+            (function_name, function_name, argument_names))
+      else:
+        file.write('  return driver_->fn.%sFn(%s);\n' %
+            (function_name, argument_names))
     file.write('}\n')
 
   # Write TraceGLApi functions

chromium/ui/gl/gl_bindings_autogen_wgl.cc

@@ -124,8 +124,10 @@ HGLRC WGLApiBase::wglCreateContextFn(HDC hdc) {
 HGLRC WGLApiBase::wglCreateContextAttribsARBFn(HDC hDC,
                                                HGLRC hShareContext,
                                                const int* attribList) {
-  return driver_->fn.wglCreateContextAttribsARBFn(hDC, hShareContext,
-                                                  attribList);
+  return driver_->fn.wglCreateContextAttribsARBFn
+             ? driver_->fn.wglCreateContextAttribsARBFn(hDC, hShareContext,
+                                                        attribList)
+             : nullptr;
 }
 
 HGLRC WGLApiBase::wglCreateLayerContextFn(HDC hdc, int iLayerPlane) {