Segmentation fault SIGSEGV

[sudharsan10]

Hey all. I am using ubuntu and I have a library provided by the manufacturer and when I tried to debug it, I got segmentation fault.

My mentor said he was able to solve it by adding the following in .pro file.
QMAKE_CXXFLAGS += -std=c++0x -pthread
LIBS += -pthread

But when I ran the same project in my PC, I still got the error but it was resolved in his PC.
Can anyone please tell me where can the problem be?

This is the function where I am getting the issue. The debugger stops at " int allocsize = strlen(key + strlen(szKey)) + 1;"

/*! Parses the configuration file

• \param szFile File name
• \param szKey Key to search for
• \param szValue Returned value (if key was found)
• \return != 0 on success /
  /*****************************************************************************/
  static int GetConfigString(const char szFile, const char* szKey, char** szValue)
  {
  int ret = 0;
  FILE* fd = fopen(szFile, "r");

if(NULL != fd)
{
/* File is open /
char buffer = malloc(PARSER_BUFFER_SIZE);

/* Read file line by line */
while(NULL != fgets(buffer, PARSER_BUFFER_SIZE, fd))
{
  char* key;

  /* '#' marks a comment line in the device.conf file */
  if(buffer[0] == '#')
    continue;

  /* Search for key in the input buffer */
  key = (char*)strcasestr(buffer, szKey);

  if(NULL != key)
  {
    /* We've found the key */
    int   allocsize  = strlen(key + strlen(szKey)) + 1;
    int   valuelen;
    char* tempstring = (char*)malloc(allocsize);

    strcpy(tempstring, key + strlen(szKey));
    valuelen = strlen(tempstring);

    /* strip all trailing whitespaces */
    while( (tempstring[valuelen - 1] == '\n') ||
           (tempstring[valuelen - 1] == '\r') ||
           (tempstring[valuelen - 1] == ' ') )
    {
      tempstring[valuelen - 1] = '\0';
      --valuelen;
    }

    *szValue = tempstring;
    ret = 1;
    break;
  }
}

free(buffer);
fclose(fd);

}

return ret;
}

[jsulm]

@sudharsan10 said in Segmentation fault SIGSEGV:

I got segmentation fault

Please post the stack trace

[sudharsan10]

Hi @jsulm Do you mean this?

[jsulm]

@sudharsan10 What is in TCP_Connector.c at line 729?
Also check your code in nextTransport_demo.c line 200
And I don't see anything related to Qt...

[sudharsan10]

You shall find line 729 in the image and also in the code I have posted above :)
I was wondering if it could be something related to my project settings, Since there was no issue while running the same project in another PC.

[JonB]

@sudharsan10

• Your question seems to have nothing at all to do with Qt.

• If the reason the changed link flags make things work is to do with pthread, you have said nothing about whether your program uses any threads.

• If any line is longer than PARSER_BUFFER_SIZE your code will not work correctly.

• int allocsize = strlen(key + strlen(szKey)) + 1;
  This line looks potentially dodgy. Print out allocsize, and consider how you are using that malloc()ed area to copy things into.

• /* strip all trailing whitespaces */
  What happens in your code if the value is all whitespace? I do not see why your should not incorrectly keep decrementing and go too far to the left, potentially overwriting unallocated memory?

• Since there was no issue while running the same project in another PC.

More likely than a project/compilation issue is that your code, somewhere, uses an uninitialized value or overwrites/underwrites a random area of memory. This can and will behave/show up differently from one PC to another, for no discernible reason....

[sudharsan10]

@JonB Thank you for pointing out at the potential problems. For now, I found it to be a project/compilation issue. I changed the compiler version to Clang just like the other PC. Also I changed the debugger settings as suggested here https://forum.qt.io/topic/100958/catching-unix-interrupt-signal-on-console-application-when-debugging-with-qtcreator/3 and it seems to work.