无法跟踪Qt程序中崩溃的原因。

Question

我们正在开发Qt中的原始数据视频播放器(https://github.com/IENT/YUView/)。我们最近遇到了一个问题，我们的球员崩溃了。我们无法在调试器中跟踪原因，它似乎发生在Qt内部的某个地方，请参见下面的跟踪。

基本上，我们有一个如何寻找问题的问题。知道该怎么处理吗？

这个问题只发生在Linux机器上(已经测试了不同的Qt版本)，而不是在Windows上。它与某些文件之间的打开和切换有关，但它只是偶尔发生，我们不能故意触发它，而必须在文件之间切换多次，直到它发生为止。可以是马上，也可以是在几分钟后。

下面是问题的线索：

0   QFontEngineFT::loadGlyphSet /usr/lib/debug/.build-id/c9/2e9e9dc3a4cf1f0133535e22d8ad76aa855d38.debug    1338    0x7fffeeed597a  
1   QFontEngineFT::loadGlyphFor /usr/lib/debug/.build-id/c9/2e9e9dc3a4cf1f0133535e22d8ad76aa855d38.debug    1795    0x7fffeeed59f8  
2   QFontEngineFT::lockedAlphaMapForGlyph   /usr/lib/debug/.build-id/c9/2e9e9dc3a4cf1f0133535e22d8ad76aa855d38.debug    1763    0x7fffeeed6ac4  
3   QRasterPaintEngine::drawCachedGlyphs    /usr/lib/debug/.build-id/81/2089dc48198b2723d82741c41011f463a732c0.debug    2760    0x7ffff75280f1  
4   QRasterPaintEngine::drawTextItem    /usr/lib/debug/.build-id/81/2089dc48198b2723d82741c41011f463a732c0.debug    3036    0x7ffff752ac5f  
5   QPainterPrivate::drawTextItem   /usr/lib/debug/.build-id/81/2089dc48198b2723d82741c41011f463a732c0.debug    6500    0x7ffff75482d1  
6   QTextLine::draw /usr/lib/debug/.build-id/81/2089dc48198b2723d82741c41011f463a732c0.debug    2532    0x7ffff73d5c5d  
7   QTextLayout::draw   /usr/lib/debug/.build-id/81/2089dc48198b2723d82741c41011f463a732c0.debug    1192    0x7ffff73d6a0d  
8   QWidgetLineControl::draw    /usr/lib/debug/.build-id/d5/2143d1747e6970d9ecdc0538c5c9170af15963.debug    629 0x7ffff7a8240b  
9   QLineEdit::paintEvent   /usr/lib/debug/.build-id/d5/2143d1747e6970d9ecdc0538c5c9170af15963.debug    1986    0x7ffff79f6038  
10  QWidget::event  /usr/lib/debug/.build-id/d5/2143d1747e6970d9ecdc0538c5c9170af15963.debug    9044    0x7ffff78e7f88  
11  QLineEdit::event    /usr/lib/debug/.build-id/d5/2143d1747e6970d9ecdc0538c5c9170af15963.debug    1456    0x7ffff79fb349  
12  QApplicationPrivate::notify_helper  /usr/lib/debug/.build-id/d5/2143d1747e6970d9ecdc0538c5c9170af15963.debug    3716    0x7ffff78a505c  
13  QApplication::notify    /usr/lib/debug/.build-id/d5/2143d1747e6970d9ecdc0538c5c9170af15963.debug    3499    0x7ffff78aa516  
14  QCoreApplication::notifyInternal    /usr/lib/debug/.build-id/53/070dadaef9fa7fb45640b17d77ee3aeeac7b13.debug    965 0x7ffff6fb238b  
15  QCoreApplication::sendSpontaneousEvent  /usr/lib/debug/.build-id/d5/2143d1747e6970d9ecdc0538c5c9170af15963.debug    227 0x7ffff78e0a79  
16  QWidgetPrivate::sendPaintEvent  /usr/lib/debug/.build-id/d5/2143d1747e6970d9ecdc0538c5c9170af15963.debug    5625    0x7ffff78e0a79  
17  QWidgetPrivate::drawWidget  /usr/lib/debug/.build-id/d5/2143d1747e6970d9ecdc0538c5c9170af15963.debug    5565    0x7ffff78e10c1  
18  QWidgetPrivate::paintSiblingsRecursive  /usr/lib/debug/.build-id/d5/2143d1747e6970d9ecdc0538c5c9170af15963.debug    5760    0x7ffff78e1d6c  
19  QWidgetPrivate::drawWidget  /usr/lib/debug/.build-id/d5/2143d1747e6970d9ecdc0538c5c9170af15963.debug    5617    0x7ffff78e0c31  
20  QWidgetPrivate::paintSiblingsRecursive  /usr/lib/debug/.build-id/d5/2143d1747e6970d9ecdc0538c5c9170af15963.debug    5760    0x7ffff78e1d6c  
21  QWidgetPrivate::paintSiblingsRecursive  /usr/lib/debug/.build-id/d5/2143d1747e6970d9ecdc0538c5c9170af15963.debug    5747    0x7ffff78e1c59  
22  QWidgetPrivate::paintSiblingsRecursive  /usr/lib/debug/.build-id/d5/2143d1747e6970d9ecdc0538c5c9170af15963.debug    5747    0x7ffff78e1c59  
23  QWidgetPrivate::paintSiblingsRecursive  /usr/lib/debug/.build-id/d5/2143d1747e6970d9ecdc0538c5c9170af15963.debug    5747    0x7ffff78e1c59  
24  QWidgetPrivate::paintSiblingsRecursive  /usr/lib/debug/.build-id/d5/2143d1747e6970d9ecdc0538c5c9170af15963.debug    5747    0x7ffff78e1c59  
25  QWidgetPrivate::paintSiblingsRecursive  /usr/lib/debug/.build-id/d5/2143d1747e6970d9ecdc0538c5c9170af15963.debug    5747    0x7ffff78e1c59  
26  QWidgetPrivate::drawWidget  /usr/lib/debug/.build-id/d5/2143d1747e6970d9ecdc0538c5c9170af15963.debug    5617    0x7ffff78e0c31  
27  QWidgetPrivate::paintSiblingsRecursive  /usr/lib/debug/.build-id/d5/2143d1747e6970d9ecdc0538c5c9170af15963.debug    5760    0x7ffff78e1d6c  
28  QWidgetPrivate::drawWidget  /usr/lib/debug/.build-id/d5/2143d1747e6970d9ecdc0538c5c9170af15963.debug    5617    0x7ffff78e0c31  
29  QWidgetPrivate::paintSiblingsRecursive  /usr/lib/debug/.build-id/d5/2143d1747e6970d9ecdc0538c5c9170af15963.debug    5760    0x7ffff78e1d6c  
30  QWidgetPrivate::drawWidget  /usr/lib/debug/.build-id/d5/2143d1747e6970d9ecdc0538c5c9170af15963.debug    5617    0x7ffff78e0c31  
31  QWidgetPrivate::paintSiblingsRecursive  /usr/lib/debug/.build-id/d5/2143d1747e6970d9ecdc0538c5c9170af15963.debug    5760    0x7ffff78e1d6c  
32  QWidgetPrivate::drawWidget  /usr/lib/debug/.build-id/d5/2143d1747e6970d9ecdc0538c5c9170af15963.debug    5617    0x7ffff78e0c31  
33  QWidgetPrivate::paintSiblingsRecursive  /usr/lib/debug/.build-id/d5/2143d1747e6970d9ecdc0538c5c9170af15963.debug    5760    0x7ffff78e1d6c  
34  QWidgetPrivate::paintSiblingsRecursive  /usr/lib/debug/.build-id/d5/2143d1747e6970d9ecdc0538c5c9170af15963.debug    5747    0x7ffff78e1c59  
35  QWidgetPrivate::paintSiblingsRecursive  /usr/lib/debug/.build-id/d5/2143d1747e6970d9ecdc0538c5c9170af15963.debug    5747    0x7ffff78e1c59  
36  QWidgetPrivate::drawWidget  /usr/lib/debug/.build-id/d5/2143d1747e6970d9ecdc0538c5c9170af15963.debug    5617    0x7ffff78e0c31  
37  QWidgetBackingStore::doSync /usr/lib/debug/.build-id/d5/2143d1747e6970d9ecdc0538c5c9170af15963.debug    1226    0x7ffff78b28aa  
38  QWidgetBackingStore::sync   /usr/lib/debug/.build-id/d5/2143d1747e6970d9ecdc0538c5c9170af15963.debug    1032    0x7ffff78b2a8c  
39  QWidgetPrivate::syncBackingStore    /usr/lib/debug/.build-id/d5/2143d1747e6970d9ecdc0538c5c9170af15963.debug    1902    0x7ffff78d0c1f  
40  QWidget::event  /usr/lib/debug/.build-id/d5/2143d1747e6970d9ecdc0538c5c9170af15963.debug    8983    0x7ffff78e7d88  
41  QMainWindow::event  /usr/lib/debug/.build-id/d5/2143d1747e6970d9ecdc0538c5c9170af15963.debug    1495    0x7ffff79fdd7b  
42  QApplicationPrivate::notify_helper  /usr/lib/debug/.build-id/d5/2143d1747e6970d9ecdc0538c5c9170af15963.debug    3716    0x7ffff78a505c  
43  QApplication::notify    /usr/lib/debug/.build-id/d5/2143d1747e6970d9ecdc0538c5c9170af15963.debug    3499    0x7ffff78aa516  
44  QCoreApplication::notifyInternal    /usr/lib/debug/.build-id/53/070dadaef9fa7fb45640b17d77ee3aeeac7b13.debug    965 0x7ffff6fb238b  
45  QCoreApplication::sendEvent /usr/lib/debug/.build-id/53/070dadaef9fa7fb45640b17d77ee3aeeac7b13.debug    224 0x7ffff6fb4786  
46  QCoreApplicationPrivate::sendPostedEvents   /usr/lib/debug/.build-id/53/070dadaef9fa7fb45640b17d77ee3aeeac7b13.debug    1593    0x7ffff6fb4786  
47  QCoreApplication::sendPostedEvents  /usr/lib/debug/.build-id/53/070dadaef9fa7fb45640b17d77ee3aeeac7b13.debug    1451    0x7ffff6fb4c68  
48  postEventSourceDispatch /usr/lib/debug/.build-id/53/070dadaef9fa7fb45640b17d77ee3aeeac7b13.debug    271 0x7ffff70083c3  
49  g_main_context_dispatch         0x7ffff57691a7  
50  ??          0x7ffff5769400  
51  g_main_context_iteration            0x7ffff57694ac  
52  QEventDispatcherGlib::processEvents /usr/lib/debug/.build-id/53/070dadaef9fa7fb45640b17d77ee3aeeac7b13.debug    418 0x7ffff70087cf  
53  QEventLoop::exec    /usr/lib/debug/.build-id/53/070dadaef9fa7fb45640b17d77ee3aeeac7b13.debug    204 0x7ffff6fafb4a  
54  QCoreApplication::exec  /usr/lib/debug/.build-id/53/070dadaef9fa7fb45640b17d77ee3aeeac7b13.debug    1229    0x7ffff6fb7bec  
55  main    yuviewapp.cpp   84  0x4b16e9    

Answer 1

QFontEngineFT::loadGlyphSet(const QTransform &matrix)发生在QT5.5中的第1338行。

1334 if (matrix.type() > QTransform::TxShear || !cacheEnabled)
1335    return 0;
1336
1337 // FT_Set_Transform only supports scalable fonts
1338 if (!FT_IS_SCALABLE(freetype->face))
1339    return matrix.type() <= QTransform::TxTranslate ? &defaultGlyphSet : Q_NULLPTR;

这是Qt中的一个bug，在QT5.7中还没有修复。然而，一个可能的解决办法是强制返回语句发生。这可以通过设置以下环境varibale来完成：

export QT_NO_FT_CACHE=1