Re: ESP not properly saved (DLL calling an exe's object function).

"David Ching" <>
Thu, 14 Jun 2007 13:15:45 GMT
"Ricardo Vazquez" <> wrote in message

This is the prototype of the function at the DLL:
  class IEventListener
   char clientId[128];

   IEventListener() {};
   virtual ~IEventListener() {};
   virtual void LockRef() = 0;
   virtual void UnlockRef() = 0;
   virtual void DeviceStatus(char * deviceId, unsigned int numCalls, long
*callStatusList) = 0;

I'm not sure it's causing the crash, but you shouldn't have data in
interfaces (such as the clientId). Interfaces should contain only abstract
virtual methods. The reason is compiler settings for things like byte
alignment, etc. can differ in modules using this interface. Data members
should only appear in implementation classes, such as your CClientThread.

Its implementation is, -within the exe file code-:
  void CClientThread::DeviceStatus(char * deviceId, unsigned int numCalls,
long *callStatusList)
   CString msg;
   CString cl, status;
   for (UINT i = 0; i < numCalls; i++) {
    status.Format("%ld", callStatusList[i]);
    cl += status;
    cl += ";";
   msg.Format("[%s, %ld] <---- DeviceStatus(%s, %d, %s)",
       clientId, clientSocket, deviceId, numCalls, cl);
   g_logSystem.logNormal(2, msg);
   msg.Format("24$%s$%d$%s", deviceId, numCalls, cl);

Calling convention in both project settings is __cdecl*

Please notice that this is not an exe calling a DLL function, but a DLL
calling an exe's object function.
And also notice that it normally runs just fine. It is only when subjected
to stress-testing, and after 20 or 30 minutes, when the error raises.

Any hints or clues on what may be happening? Why do I get that "ESP not
properly saved" after hundreds of calls?

Well, since the call works even once, it's obviously not a calling
convention problem because it would have been caught the very first time.
But I think the way this works is that code is injected by the compiler to
compare the value of ESP register before function call and after function
returns. If they're not the same, the error is generated. I think what's
happening is the callstack is getting screwed up (stack overwrites of local
variables?) and the return address is slightly altered so that the code that
generates the error is jumped to arbitrarily.

Are you comfortable in the Disassembler window?

Since you log each call to DeviceStatus(), is there anything special about
the parameters when it crashes? Also, what does send() do? Maybe that is
screwing up the stack somehow.

The way to debug these problems is methodically remove functionality until
the crash stops, and go from there. I would try to remove send() and see if
you can repro it.

-- David

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