valgrind warning in Qt

[vitaly]

I use Qt 3.3.2, gcc 3.3.3. I wrote simple xml parsing test.



#include <qxml.h>

int main( int argc, char** argv)
{
QString s = "<xml></xml>";

QXmlInputSource input;
input.setData(s);

QXmlSimpleReader reader;
if (!reader.parse(&input, FALSE))
return 1;

return 0;
}


If to compile this test and run under valgrind the following warning will be shown:

==10134== Conditional jump or move depends on uninitialised value(s)
==10134== at 0x446B9CE: QXmlSimpleReader::parseElement() (in /usr/local/qt-3.3.2-3.3.3/lib/libqt-mt.so.3.3.2)
==10134== by 0x446B200: QXmlSimpleReader::parseBeginOrContinue(int, bool) (in /usr/local/qt-3.3.2-3.3.3/lib/libqt-mt.so.3.3.2)
==10134== by 0x446AEE1: QXmlSimpleReader::parse(QXmlInputSource const*, bool) (in /usr/local/qt-3.3.2-3.3.3/lib/libqt-mt.so.3.3.2)
==10134== by 0x8048D52: main (main.cpp:<this line number points to reader.parse(..) string)

Is it Qt bug and how to avoid it?

Thanks,
Vitaly

[jpn]

If to compile this test and run under valgrind the following warning will be shown:

==10134== Conditional jump or move depends on uninitialised value(s)
==10134== at 0x446B9CE: QXmlSimpleReader::parseElement() (in /usr/local/qt-3.3.2-3.3.3/lib/libqt-mt.so.3.3.2)
==10134== by 0x446B200: QXmlSimpleReader::parseBeginOrContinue(int, bool) (in /usr/local/qt-3.3.2-3.3.3/lib/libqt-mt.so.3.3.2)
==10134== by 0x446AEE1: QXmlSimpleReader::parse(QXmlInputSource const*, bool) (in /usr/local/qt-3.3.2-3.3.3/lib/libqt-mt.so.3.3.2)
==10134== by 0x8048D52: main (main.cpp:<this line number points to reader.parse(..) string)

Is it Qt bug and how to avoid it?
There's not much you can do about it, unless you stab the QXmlSimpleReader sources. ;) Valgrind just doesn't like the way it is written..

[Mad Max]

You can use valgrind's options "gen-suppressions" and "suppressions" to suppress any errors which are not interesting for you.


# valgrind --gen-suppressions=yes ./app
# valgrind --suppressions=suppressions.err ./app

[vitaly]

Thanks for reply!

My project has only this Valgrind warning at the moment. But our QA group doesn't like it. They suspect me of making a bug. I thought to investigate the problem but it may need much timе. With high probability (and with your help in answering me, of course) I suspect Qt in this warning, so I will demonstrate our QA that it is not my "bug" by presenting the test described above.

Thanks a lot
Vitaly

[wysota]

It's not really a bug. Valgrind is too stupid to guess from the context that the variable will be initialised. Take this example:


int i;
if(something){
i=7;
}
if(!something){
i=5;
}
if(i==5){
// ...
} else {
// ...
}

Now from machine's point of view, i may be uninitialised during "if(i==5)" test, but based on the context you'll notice that i will always be initialised, either as 7 or as 5. So there's no bug here. And this could and probably is the same case with the xml parser.