QT deployed executable crashes on some computers

JonB

@hskoglund
I noted that too. But users says only happens when network cable unplugged! Normally he gets a 0xc0000008 rather than a 0xc0000007b . Strange how that could lead to 32-/64-bit issue?!

Lati

@JonB No no, I haven't said it happens only when network cable is unplugged. It happens always with or without internet connection.

@hskoglund I wonder if this is the reason because I use the same deployment on all computers. But, I will check that again.

I hope I can solve this "mystery" soon :/

JonB

@Lati

@JonB No no, I haven't said it happens only when network cable is unplugged. It happens always with or without internet connection.

Read what you have posted and you do seem to say what I wrote. First earlier:

Exception code: 0xc0000008

then later screenshot

0xc0000007b

It's what you have pasted!

Anyway, if you Google for the 0xc0000007b you will come across 32-/64-bit mis-match. I am not certain whether that always applies, but worth investigating.

Lati

@JonB @hskoglund
Nope, I have re-deployed using windeployqt.exe and copied the necessary dlls from SysWOW64 (again) and still have the same problem.

To summarize: I deployed the application created using QT Creator and test the executable on different computers. Deployed files are same on 6 different computers. Executable runs on three computers without any issue and crashes on other three without any indication.

Additionally, I uninstalled all VC++ Runtime installations on one of the computer and installed the ones in the "C:\Qt\vcredist" and still have the same problem.

hskoglund

If you have 2 computers pretty near each other, and one of them is of the crashing kind and the other is one the healthy ones, try swapping the network cables, i.e. unplug the network cable going to the healthy PC and instead plug it into the crashing PC, and the other way around.

fcarney

A couple thoughts:

Make sure you are running the correct version of the deploy tool. I had issues with my deploys where I was running it under the 5.12.2 console when I should be running it under the 5.12.5 console.
Check for race conditions on when your web data arrives. Is your app relying on the data it grabs and if it doesn't get it in time it will cause a crash.

Lati

Ok. I decided to install the Qt on one of the computer where executable crashes. I copied the whole development folder and build the application. I can build the application in Debug and Release without any problem. However, when I try to start the debug with F5, I get following error:

Please note that Qt is installed on D drive. I tried few solutions offered by Google, like copying the Qt dll's in the debug folder which didn't help. I feel very desperate.

@hskoglund
Pc's are a bit far from each other :) I use remote desktop most of the time.

@fcarney
I checked that, it is v 5.12.1. I don't know how to be sure which version it should be.

Lati

Finally! I found where the problem is. I received source code of the one of the libraries I use. And there is following code in the library:

programXRootDirectory = getenv("ProgramXROOT");

And yes, if the environmental variable doesn't exist, executable crashes. Strangely, there is no sign about the crash caused by getenv.

I will keep this thread, maybe someone else has the same problem.

I would like to thank you everyone who tried to help me so far!

Update:getenv is deprecated and _dupenv_s recommended instead. More information about _dupenv_s

Pablo J. Rogina

@Lati said in QT deployed executable crashes on some computers:

Strangely, there is no sign about the crash caused by getenv.

Well, it looks like the culprit isn't getenv() but the way the return value from that function is used within the DLL later on. From man getvenv:

The getenv() function returns a pointer to the value in the environment, or NULL if there is no match.

so programXRootDirectory becomes NULL when the variable is not set, and the world ends...

JonB

@Lati
That file error screenshot is in Qt5Cored.dll. Note the d at the end of the name. That is the version compiled for debug (plus the message). Why are you deploying debug DLLs?

It would be interesting to see whether the problem across different PCs even occurs any more if you compiled & released for Release instead?

getenv does not crash when an environment variable does not exist, it returns NULL. If the code fails to deal with that (e.g. dereferences), that's a different matter, and is the only way it could "crash". So you have verified that the environment variable named ProgramXROOT does not/does exist on the machines which crash/don't crash respectively?

Lati

@Pablo-J-Rogina
Exactly! No-one would guess the crash is due to getenvsince all indications were showing that it was either false libraries or graphic card issue.

@JonB
I am not deploying anything on that screen. The screenshot is after I clicked on F5 to debug the code and the path of the Qt5Cored.dll is from Qt's installation directory (Qt is installed on D: drive, as I mentioned). getenv crashes on my computer, as well as the deployed executable crashes on the computers if the environmental variable doesn't exist. It is very easy to test by writing a small application.

JonB

@Lati said in QT deployed executable crashes on some computers:

It is very easy to test by writing a small application.

char *p = getenv("ProgramXROOT");
// or
char *p = getenv("AnythingElseWhichDoesntExist");

won't crash. It will set p to NULL/nullptr.

If the program continues and does not check for that, assuming that p will not be null, it may crash. That is all @Pablo-J-Rogina and I are saying.

fcarney

@Lati said in QT deployed executable crashes on some computers:

programXRootDirectory

It would be interesting to know what the data type is for this variable. I could not get QString to crash or misbehave.

{
        char* null = nullptr;

        QString test = "hallo";
        qInfo() << "before init null";
        test = QString(null);
        qInfo() << test;
        qInfo() << "after init null";

        QString test2 = "hallo again";
        qInfo() << "before assign null";
        test2 = null;
        qInfo() << test2;
        qInfo() << "after assign null";
    }

Lati

@fcarney
You can reproduce the issue with the following example (at least it crashes on my computer:)):

main.cpp

#include "mainwindow.h"
#include <QApplication>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    MainWindow w;
    w.show();
    return a.exec();
}

mainWindow.h:

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>

QT_BEGIN_NAMESPACE
namespace Ui { class MainWindow; }
QT_END_NAMESPACE

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    MainWindow(QWidget *parent = nullptr);
    ~MainWindow();

    // Senex root directory
    std::string notExistEnvVar;

private:
    Ui::MainWindow *ui;
};
#endif // MAINWINDOW_H

mainWindow.cpp

#include "mainwindow.h"
#include "ui_mainwindow.h"

MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
    , ui(new Ui::MainWindow)
{
    ui->setupUi(this);

    notExistEnvVar = getenv("notExistEnvVar");
}

MainWindow::~MainWindow()
{
    delete ui;
}

Compiled with MSVC2015 64bit.

fcarney

You are getting an exception because you are assigning nullptr to std::string. Assign to

char* ptr = getenv("notExistEnvVar");
if(ptr != nullptr)
  notExistEnvVar = ptr;

getenv is not crashing

Edit:
or use QString

QString str = getenv("notExistEnvVar");

JonB

@fcarney Thank you :)

JonB

For std::string s = nullptr, see https://stackoverflow.com/questions/10771864/assign-a-nullptr-to-a-stdstring-is-safe/10771938. Accepted answer:

Requires: s shall not be a null pointer.

Since the standard does not ask the library to throw an exception when this particular requirement is not met, it would appear that passing a null pointer provoked undefined behavior.

fcarney

@JonB said in QT deployed executable crashes on some computers:

undefined

!!!UNDEFINED!!!
The end is nigh!

Good find!

Pablo J. Rogina

@JonB said in QT deployed executable crashes on some computers:

won't crash. It will set p to NULL/nullptr.

The problem is not the assignment... the problem comes once you have assigned NULL to the pointer and then you try using it

Lati

@fcarney

Obviously, the person who wrote the library didn't know this (to be honest, I didn't know it as well, I have never used getenv). And this is how bugs happened, right? :)

But interesting thing is that there is no sign about the crash and no-one had an idea about it (including me). I would still look at the error somewhere else if I wouldn't test the code on one of the problem computer.

Anyway, thank you for the clarification.