See here:
http://paste.ubuntu.com/16343869/
this is the relevant code from qsgthreadedrendererloop.cpp:
if (!w->thread->gl) {
w->thread->gl = new QOpenGLContext();
if (qt_gl_global_share_context())
w->thread->gl->setShareContext(qt_gl_global_share_context());
w->thread->gl->setFormat(w->window->requestedFormat());
w->thread->gl->setScreen(w->window->screen());
if (!w->thread->gl->create()) {
const bool isEs = w->thread->gl->isOpenGLES();
delete w->thread->gl;
w->thread->gl = 0;
handleContextCreationFailure(w->window, isEs);
return;
}
Qt is creating a GL context object, but creation fails. In cleaning up, QtUbuntu crashes as it's tries to release an invalid context.
FWIW
(gdb) print mEglDisplay
$1 = (EGLDisplay) 0x9de8ad8
(gdb) print mEglContext
$2 = (EGLContext) 0x0