QString constructor segfault. qshaderdescription.cpp corruption

ridderhoff

A few function calls past our main function a QString gets constructed and segfaults with the following stack trace

(gdb) bt
#0  0x000000000044d60b in int QAtomicOps<int>::loadRelaxed<int>(std::atomic<int> const&) ()
#1  0x000000000044ceb8 in QBasicAtomicInteger<int>::loadRelaxed() const ()
#2  0x000000000044c46e in QtPrivate::RefCount::ref() ()
#3  0x000000000044ca67 in QString::QString(QString const&) ()
...

I assumed that our project was doing something unsafe with memory and recompiled with libefence so that I could figure out what was causing the problem.

(gdb) bt
#0  QString::fromLatin1_helper (str=str@entry=0x7ffff5b6562b "float", size=size@entry=5) at text/qstring.cpp:5462
#1  0x00007ffff563ac75 in QString::QString (aLatin1=..., this=0x7ffff5e7d7c0 <typeTab>)
    at ../../include/QtCore/../../src/corelib/text/qstring.h:1067
#2  __static_initialization_and_destruction_0 (__initialize_p=1, __priority=65535) at rhi/qshaderdescription.cpp:666
#3  _GLOBAL__sub_I_qshaderdescription.cpp(void) () at rhi/qshaderdescription.cpp:1513
#4  0x00007ffff7de3e0a in call_init (l=<optimized out>, argc=argc@entry=1, argv=argv@entry=0x7fffffffdbd8, env=env@entry=0x7fffffffdbe8)
    at dl-init.c:72
#5  0x00007ffff7de3f0a in call_init (env=0x7fffffffdbe8, argv=0x7fffffffdbd8, argc=1, l=<optimized out>) at dl-init.c:30
#6  _dl_init (main_map=0x7ffff7ffe1f0, argc=1, argv=0x7fffffffdbd8, env=0x7fffffffdbe8) at dl-init.c:119
#7  0x00007ffff7dd501a in _dl_start_user () from /lib64/ld-linux-x86-64.so.2

This suggests that the problem is the result of a static variable in the gui/rhi component using QStrings as static variables before they're ready. Checking git I found that these keys were changed to const char* and this change/fix should be live in recent versions of Qt 6.

Apart from upgrading our entire software to Qt 6 is there anything I can do to make this work? I feel like if the issue should be experienced by more Linux developers since as far as I know we're not actually using any of the features in RHI directly. We currently have software working with Qt 5.15.2 on Windows but struggling with the Linux port.

SGaist

Hi and welcome to devnet,

Can you trigger that with a minimal compilable example ?