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Details

Type: Bug
Resolution: Done
Priority: P3: Somewhat important
Fix Version/s: 5.8.0
Affects Version/s: 5.5.1
Component/s: Core: Plugins
Labels:
None
Environment:
Qt 5.5

Commits:
494376f980e96339b6f1eff7c41336ca4d853065

Description

In LXQt we were facing a SEGFAULT in static finalization time (in QString destructor). Finaly we've got through to this scenario:

dynamicaly loaded library lib2 uses library lib1 by passing it QString& constructed by QStringLiteral
library lib1 stores the (copy of) passed QString in static container
after application termination the program crashes in static finalization of library lib1

Test case is attached (together with cmake build instructions) -> the code is simple:

buglib1.cpp

#include <QString>

static QString static_storage;

void buglib1_call(QString const & str)
{
    static_storage = str;
}

buglib2.cpp

#include <QString>

extern void buglib1_call(QString const & str);

extern "C"
{
void buglib2_call()
{
    buglib1_call(QStringLiteral("test"));
}
}

main.cpp

#include <dlfcn.h>
#include <iostream>

typedef void func_t();
int main(int argc, char * argv[])
{
    void * h = dlopen("./libbuglib2.so", RTLD_LAZY);
    if (nullptr == h)
    {
        std::cerr << dlerror() << std::endl;
        return 1;
    }

    func_t * fun = reinterpret_cast<func_t *>(dlsym(h, "buglib2_call"));
    if (nullptr == fun)
    {
        std::cerr << dlerror() << std::endl;
        return 1;
    }

    (*fun)();

    dlclose(h);
    return 0;
}

This is the backtrace of crash:

#0  0x00007f44533fdf84 in QGenericAtomicOps<QBasicAtomicOps<4> >::load<int> (_q_value=@0x7f444ee18178: <error reading variable>) at /usr/include/x86_64-linux-gnu/qt5/QtCore/qgenericatomic.h:90
#1  QBasicAtomicInteger<int>::load (this=0x7f444ee18178) at /usr/include/x86_64-linux-gnu/qt5/QtCore/qbasicatomic.h:118
#2  0x00007f44533fdec9 in QtPrivate::RefCount::deref (this=0x7f444ee18178) at /usr/include/x86_64-linux-gnu/qt5/QtCore/qrefcount.h:60
#3  0x00007f44533fde7f in QString::~QString (this=0x7f44535fe5e0 <static_storage>) at /usr/include/x86_64-linux-gnu/qt5/QtCore/qstring.h:1053
#4  0x00007f445211ef4f in __cxa_finalize (d=0x7f44535fe5c8) at cxa_finalize.c:56
#5  0x00007f44533fddb3 in __do_global_dtors_aux () from /home/palco/work/oss/qstring_bug/build/libbuglib1.so
#6  0x00007ffc17b4f720 in ?? ()
#7  0x00007f445360e01a in _dl_fini () at dl-fini.c:252

This seems to be a bug in the QString copy/move (over)optimization and/or the QPluginLoader (we are observing this behaviour in libraries loaded by QPluginLoader).

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plugin_report.tar
10 kB
12 Nov '15 19:46
report.tar
10 kB
27 Oct '15 22:45

Issue Links

duplicates

QTBUG-62625 App crashes on termination if a font is loaded by unloaded library

Closed

is duplicated by

QTBUG-49792 QStringLiteral iniside a Plugin crashes after the plugin was unloaded

Closed

replaces

QTBUG-50829 Segfault during application's exit with static QIcon instances due to a QIconEngine plugin being unloaded too early

Closed

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For Gerrit Dashboard: QTBUG-49061
#	Subject	Branch	Project	Status	CR	V
140750,4	Stop unloading plugins in QPluginLoader and QFactoryLoader	dev	qt/qtbase	Status: MERGED	+2	0
172014,2	Stop unloading plugins in QPluginLoader and QFactoryLoader	5.6	qt/qtbase	Status: ABANDONED	-2	0
174911,2	Stop unloading plugins in QPluginLoader and QFactoryLoader	5.6	qt/qtbase	Status: MERGED	+2	0