segmentation fault in QTextDocument::print

I met a very strange segfault and I does not understand the cause.

Context: in a console QT application, I need to create a PDF file containing some information but the PDF generation causes a segmentation fault. I reduced the initial code to the main function and a method.

The qt .pro file:

CONFIG   += console
CONFIG   -= app_bundle
TEMPLATE = app
QT  += core
QT  += gui # need for pdf generation
QT  += printsupport #need for pdf generation

main.cpp

int main(int argc, char *argv[])
{
    QCoreApplication::setSetuidAllowed(true);
    QCoreApplication app(argc, argv);
    CPdfCreationDryRun pdfCreate(&app);
    QTimer::singleShot(0, &pdfCreate, SLOT(start()));
    return app.exec();
}

test.cpp

void CPdfCreationDryRun::start()
{
    QTextDocument doc {};
    const QString msg {"<p>toto</p>"};
    const QString pdfFileName {"toto.pdf"};

    QPrinter printer {QPrinter::PrinterResolution};
    printer.setPageSize(QPrinter::A4);
    printer.setOrientation(QPrinter::Portrait);
    printer.setOutputFormat(QPrinter::PdfFormat);
    printer.setOutputFileName(pdfFileName);
    printer.setFontEmbeddingEnabled(true);

    doc.print(&printer);
}

gdb backtrace

#0  0x00007f5cfec7bc42 in ?? () from /usr/lib/x86_64-linux-gnu/libQt5Gui.so.5
#1  0x00007f5cfec7f2cd in QFontDatabase::findFont(QFontDef const&, int) () from /usr/lib/x86_64-linux-gnu/libQt5Gui.so.5
#2  0x00007f5cfec7faf6 in QFontDatabase::load(QFontPrivate const*, int) () from /usr/lib/x86_64-linux-gnu/libQt5Gui.so.5
#3  0x00007f5cfec553b3 in QFontPrivate::engineForScript(int) const () from /usr/lib/x86_64-linux-gnu/libQt5Gui.so.5
#4  0x00007f5cfec86cf9 in ?? () from /usr/lib/x86_64-linux-gnu/libQt5Gui.so.5
#5  0x00007f5cfeca0006 in QTextLine::layout_helper(int) () from /usr/lib/x86_64-linux-gnu/libQt5Gui.so.5
#6  0x00007f5cfeca1840 in QTextLine::setLineWidth(double) () from /usr/lib/x86_64-linux-gnu/libQt5Gui.so.5
#7  0x00007f5cfece4d3d in ?? () from /usr/lib/x86_64-linux-gnu/libQt5Gui.so.5
#8  0x00007f5cfece5845 in ?? () from /usr/lib/x86_64-linux-gnu/libQt5Gui.so.5
#9  0x00007f5cfeceac3d in ?? () from /usr/lib/x86_64-linux-gnu/libQt5Gui.so.5
#10 0x00007f5cfeceb0b9 in ?? () from /usr/lib/x86_64-linux-gnu/libQt5Gui.so.5
#11 0x00007f5cfeceb2b8 in QTextDocumentLayout::doLayout(int, int, int) () from /usr/lib/x86_64-linux-gnu/libQt5Gui.so.5
#12 0x00007f5cfecebde1 in ?? () from /usr/lib/x86_64-linux-gnu/libQt5Gui.so.5
#13 0x00007f5cfecec789 in QTextDocumentLayout::documentChanged(int, int, int) () from /usr/lib/x86_64-linux-gnu/libQt5Gui.so.5
#14 0x00007f5cfecb6bc6 in QTextDocument::documentLayout() const () from /usr/lib/x86_64-linux-gnu/libQt5Gui.so.5
#15 0x00007f5cfecbe1ed in QTextDocument::print(QPagedPaintDevice*) const () from /usr/lib/x86_64-linux-gnu/libQt5Gui.so.5
#16 0x0000559445993520 in CPdfCreationDryRun::start (this=0x7ffc7ea14be0) at

valgrind logs:

==82570== Invalid read of size 8
==82570==    at 0x54A8C42: ??? (in /usr/lib/x86_64-linux-gnu/libQt5Gui.so.5.9.5)
==82570==    by 0x54AC2CC: QFontDatabase::findFont(QFontDef const&, int) (in /usr/lib/x86_64-linux-gnu/libQt5Gui.so.5.9.5)
==82570==    by 0x54ACAF5: QFontDatabase::load(QFontPrivate const*, int) (in /usr/lib/x86_64-linux-gnu/libQt5Gui.so.5.9.5)
==82570==    by 0x54823B2: QFontPrivate::engineForScript(int) const (in /usr/lib/x86_64-linux-gnu/libQt5Gui.so.5.9.5)
==82570==    by 0x54B7617: QTextEngine::fontEngine(QScriptItem const&, QFixed*, QFixed*, QFixed*) const (in /usr/lib/x86_64-linux-gnu/libQt5Gui.so.5.9.5)
==82570==    by 0x54B8708: QTextEngine::shapeText(int) const (in /usr/lib/x86_64-linux-gnu/libQt5Gui.so.5.9.5)
==82570==    by 0x54B93EE: QTextEngine::shape(int) const (in /usr/lib/x86_64-linux-gnu/libQt5Gui.so.5.9.5)
==82570==    by 0x54CDDFB: QTextLine::layout_helper(int) (in /usr/lib/x86_64-linux-gnu/libQt5Gui.so.5.9.5)
==82570==    by 0x54CE83F: QTextLine::setLineWidth(double) (in /usr/lib/x86_64-linux-gnu/libQt5Gui.so.5.9.5)
==82570==    by 0x5511D3C: ??? (in /usr/lib/x86_64-linux-gnu/libQt5Gui.so.5.9.5)
==82570==    by 0x5512844: ??? (in /usr/lib/x86_64-linux-gnu/libQt5Gui.so.5.9.5)
==82570==    by 0x5517C3C: ??? (in /usr/lib/x86_64-linux-gnu/libQt5Gui.so.5.9.5)
==82570==  Address 0x0 is not stack'd, malloc'd or (recently) free'd
==82570== 
==82570== 
==82570== Process terminating with default action of signal 11 (SIGSEGV)
==82570==  Access not within mapped region at address 0x0
==82570==    at 0x54A8C42: ??? (in /usr/lib/x86_64-linux-gnu/libQt5Gui.so.5.9.5)
==82570==    by 0x54AC2CC: QFontDatabase::findFont(QFontDef const&, int) (in /usr/lib/x86_64-linux-gnu/libQt5Gui.so.5.9.5)
==82570==    by 0x54ACAF5: QFontDatabase::load(QFontPrivate const*, int) (in /usr/lib/x86_64-linux-gnu/libQt5Gui.so.5.9.5)
==82570==    by 0x54823B2: QFontPrivate::engineForScript(int) const (in /usr/lib/x86_64-linux-gnu/libQt5Gui.so.5.9.5)
==82570==    by 0x54B7617: QTextEngine::fontEngine(QScriptItem const&, QFixed*, QFixed*, QFixed*) const (in /usr/lib/x86_64-linux-gnu/libQt5Gui.so.5.9.5)
==82570==    by 0x54B8708: QTextEngine::shapeText(int) const (in /usr/lib/x86_64-linux-gnu/libQt5Gui.so.5.9.5)
==82570==    by 0x54B93EE: QTextEngine::shape(int) const (in /usr/lib/x86_64-linux-gnu/libQt5Gui.so.5.9.5)
==82570==    by 0x54CDDFB: QTextLine::layout_helper(int) (in /usr/lib/x86_64-linux-gnu/libQt5Gui.so.5.9.5)
==82570==    by 0x54CE83F: QTextLine::setLineWidth(double) (in /usr/lib/x86_64-linux-gnu/libQt5Gui.so.5.9.5)
==82570==    by 0x5511D3C: ??? (in /usr/lib/x86_64-linux-gnu/libQt5Gui.so.5.9.5)
==82570==    by 0x5512844: ??? (in /usr/lib/x86_64-linux-gnu/libQt5Gui.so.5.9.5)
==82570==    by 0x5517C3C: ??? (in /usr/lib/x86_64-linux-gnu/libQt5Gui.so.5.9.5)

I tried to redefine QT_QPA_FONTDIR env variable to different directories containing fonts but this did not change the behavior.

Host configuration:

Linux ubuntu 4.18.0-25-generic #26~18.04.1-Ubuntu SMP Thu Jun 27 07:28:31 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux

g++ --version g++ (Ubuntu 8.3.0-6ubuntu1~18.04.1) 8.3.0

QT: 5.9.5-0ubuntu1

I am looking for any helps to understand the observed behavior and how to fix it.

Thanks & regards,