“Run-Time Check Failure #0 - The value of ESP was

Question

I'm making a C# application which is using GameSpy C code (the GP part). The C code is calling a callback (which is C# code) succesfully, but I get this error Run-Time Check Failure #0 - The value of ESP was not properly saved across a function call right after the callback is done. I've made a DLL out of C code, like this:

    // GPCallback
    /////////////
    __declspec(dllexport) typedef void (* GPCallback)(
      GPConnection * connection,
      void * arg,
      void * param
    );

    // gpConnect
    ////////////
    __declspec(dllexport) GPResult gpConnect
    (
      GPConnection * connection,
      const gsi_char nick[GP_NICK_LEN],
      const gsi_char email[GP_EMAIL_LEN],
      const gsi_char password[GP_PASSWORD_LEN],
      GPEnum firewall,
      GPEnum blocking,
      GPCallback callback,
      void * param
    );

C# is calling it like this:

   unsafe public delegate void GPCallback(
   GPConnection * connection,
   //GPConnectResponseArg arg,
   IntPtr arg,
   IntPtr param
  );

  [DllImport("saketestd.dll")]
  unsafe static extern GPResult gpConnect(
   GPConnection * connection, 
   gsi_char nick, 
   gsi_char email, 
   gsi_char password, 
   GPEnum firewall,
   GPEnum blocking,
   GPCallback callback,
   IntPtr param
  );
  unsafe public bool gpConnectE() {
   bool ret = false;
   try {
    GPResult res;
    debug.AddLine(this.getMethodName() + ": " + "connection before connect: " + connection.ToString("x"));
    fixed (int* pconn = &connection) {
     res = gpConnect(
      pconn,
      this.NICK,
      this.EMAIL,
      this.PASSWORD,
      GPEnum.GP_NO_FIREWALL,
      GPEnum.GP_BLOCKING,
      new GPCallback(this.ConnectResponse),
      IntPtr.Zero
     );
    }
    debug.AddLine(this.getMethodName() + ": " + "connection after connect: " + connection.ToString("x"));
    if (res != GPResult.GP_NO_ERROR) {
     debug.AddLine(this.getMethodName() + ": " + "failed: " + res);
    } else {
     debug.AddLine(this.getMethodName() + ": " + "OK");
     ret = true;
    }
   } catch (Exception ex) {
    debug.Text += ex.ToString();
   }
   return ret;
  }

  unsafe public void ConnectResponse(
   GPConnection * connection,
   //GPConnectResponseArg arg,
   IntPtr argPtr,
   IntPtr param
  ) {
   debug.AddLine(this.getMethodName() + " called with connection: " + (*connection).ToString("x"));
   GPConnectResponseArg arg;
   arg = (GPConnectResponseArg)Marshal.PtrToStructure(argPtr, typeof(GPConnectResponseArg)); 
   if (arg.result == GPResult.GP_NO_ERROR) {
    debug.AddLine(this.getMethodName() + ": Connected to GP");
    this.profileid = arg.profile;
   } else {
    debug.AddLine(this.getMethodName() + ": failed");
    debug.AddLine(this.getMethodName() + ": result: " + arg.result);
    debug.AddLine(this.getMethodName() + ": profile: " + arg.profile);
    debug.AddLine(this.getMethodName() + ": uniquenick: " + arg.uniquenick);
   }
  }

I believe that I need to clear the stack in my callback or change the calling convention in the DLL (is that possible?). Any other ideas?

Answer 1

Problem solved unexpectedly my myself (after 5 hours googling). I suspected a wrong calling convention already, but I didn't know how to switch it correctly. I've changed it in the C code as suggested here (http://computerarts.com.cn/dotnet-tech/1691/):

// GPCallback
/////////////
//__declspec(dllexport) typedef void (* GPCallback)(
//typedef __declspec(dllexport) void (* GPCallback)(
typedef void (_stdcall * GPCallback)(
  GPConnection * connection,
  void * arg,
  void * param
);

Answer 2

Check the calling conventions you are using.

 [UnmanagedFunctionPointer(CallingConvention.Cdecl)]

Reference to other related question: Callback from C function - crash