Question

I’m using ChangeServiceConfig2 API of windows to change the service description. Since the same api is not supported in windows 98, ME I have used LoadLibraray and GetProcAddress to prevent static linking of the API in the exe. Please refer the code for more details:

typedef BOOL  (*ChgSvcDesc) (SC_HANDLE hService, DWORD dwInfoLevel, LPVOID lpInfo);

eBool ServiceConfigNT::Install(IN tServiceDesc * pServiceDesc){


    SC_HANDLE           hservice;
    SC_HANDLE           hservicemgr;
    SERVICE_DESCRIPTION desc;
    ULong             starttype;
    HMODULE           hmod;
    ChgSvcDesc        fpsvcdesc;

// Opens the Service Control Manager
hservicemgr = OpenSCManager(NULL, NULL, SC_MANAGER_ALL_ACCESS);
if(!hservicemgr){
    vPrepareError(_TEXT("Failed to open service control manager!!"));
    goto err;
}

// Set start method of service.
starttype   = (pServiceDesc->uAutoStart  == TRUE)? SERVICE_AUTO_START : SERVICE_DEMAND_START;

// Create the service
hservice =  CreateService(hservicemgr, vServiceName, pServiceDesc->uDisplayName, SERVICE_ALL_ACCESS, 
                pServiceDesc->uServiceType, starttype, SERVICE_ERROR_NORMAL,pServiceDesc->uExePath,
                NULL, NULL, NULL, NULL, NULL);

if(!hservice) {
    vPrepareError(_TEXT("Failed to create service.!!"));
    goto err;        
}

// Set the description string
if(pServiceDesc->uServiceDescription && *pServiceDesc->uServiceDescription) {     
    desc.lpDescription = pServiceDesc->uServiceDescription;
    // This cannot be executed since it is not supported in Win98 and ME OS
    //(Void)ChangeServiceConfig2 (hservice, SERVICE_CONFIG_DESCRIPTION, &desc);
    hmod = LoadLibrary(_TEXT("Advapi32.dll"));
    if(hmod) {
          // _UNICODE macro is set, hence im using the "W" version of the api
          fpsvcdesc = (ChgSvcDesc)GetProcAddress(hmod, "ChangeServiceConfig2W");      
          if(fpsvcdesc)
               // On execution of the below statement, I get the error handle is invalid
               fpsvcdesc(hservice, SERVICE_CONFIG_DESCRIPTION, &desc);
}

CloseServiceHandle(hservice);
CloseServiceHandle(hservicemgr);    
return TRUE;

err:
    if(hservicemgr) 
       CloseServiceHandle(hservicemgr);
return FALSE;
}

I debugged the code many times to find out why I am getting handle is invalid error ? On calling the API directly the description of service is changing but using the function pointer it gives the error.

I think that the API is writing something to the service handle of the SCM, but I have no clues as to why ?

Can somebody help me with this ?

Answer 1

Your function pointer is declared with no calling convention specified. The default calling convention is __cdecl. But Windows API functions are __stdcall. You need to add the calling convention to your function pointer type.

typedef BOOL (__stdcall *ChgSvcDesc) (SC_HANDLE hService, 
    DWORD dwInfoLevel, LPVOID lpInfo);