[Qt-interest] [Qt-embedded-interest] QProcess::execute() results in arbitrary "segmenation faults" or "illegal instructions"

[Markus Franke]

Hi Rohan,

thanks for your reply.

Well, I agree with you that it's quiet hard to determine the cause of the 
problem having just a couple of lines of code.

So far I determined that the application crashes at this line 
(QProcess::execute()) of code by using qDebug() before and after the 
function call. 
Furthermore, I now found out that removing a usleep() function call in 
another thread solves or at least avoids the problem. I am still stuck and 
don't have clue what might cause this behaviour.

I also tried to catch the "Segmentation Fault" with gdb in order to get a 
backtrace but once the application crashed gdb simply says "No stack" when 
trying to retrieve the stack via "bt".

What do you mean by "calling through a dangling pointer"? I printed the 
pointer of the object to which getLanguageUpdates() belongs to and 
everything seems to be allright. Also the object never get's destroyed as 
far as I can see.

Thanks for any comments on this,

Markus

Rohan McGovern <rohan.mcgovern at nokia.com> schrieb am 05.07.2010 03:02:53:

> On Thursday 01 July 2010, ext Markus Franke wrote:
> > Dear all,
> >
> > I am observing a strange behaviour of the QProcess::execute()
> > function resulting in segmentation faults.
> >
> > I have an object (see sample code below) which installs a timer.
> > The timer function is called every 100ms and executes within a
> > loop an external process with the help of the QProcess::execute()
> > function.
> >
> > For a couple of minutes everything is working fine and the
> > processes are being executed. But then, at some point in time my
> > whole application crashes with a "Segmentation fault" or "Illegal
> > instruction" right before or just after the call to
> > QProcess::execute().
> 
> Hi Markus,
> 
> Unfortunately there's an infinite amount of coding errors which 
> could cause this and the code you pasted isn't precise enough to 
> determine which one is causing the problem :-(
> 
> For example, you could be calling getLanguageUpdates through a 
> dangling pointer.
> 
> I think you should use general debugging techniques to determine the 
> problem, and if you want help with your code again, you should at 
> least describe how it is that you know the application is crashing 
> before or after QProcess::execute();
> 
> Also, for getting help with code, I think you'll get faster 
> turnaround asking for help on #qt on IRC (freenode) :-)
> 
> -- 
> Rohan



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