I am working on a Qt DLL that is used as a plugin for a large application. This DLL depends on other DLLs that are sadly not located in the same folder and hence will only load if the current working directory has been set correctly (which the large application does prior to calling LoadLibrary on the DLL). I have no control over this behaviour.
I have been asked to add a simple COM object to this plugin which I have done but I now have the problem that the DLL cannot be registered or used by a 3rd-party application unless the current working directory is set correctly - because any LoadLibrary calls on the plugin fail due to the missing dependencies. Obviously I have no control over the current working directory used by 3rd-party apps and at this stage I am not allowed to modify the PATH to ensure the dependencies can be found.
I have tried using /DELAYLOAD for the dependent DLLs but this fails with 'cannot delay-load foo.dll due to import of data symbol...' errors. Again, I cannot easily change the way these dependent DLLs are used.
Currently I think the only solution is to move the COM object into a stand-alone DLL that doesn't depend on anything else but I am under pressure to find a solution and leave the COM object in the plugin DLL. I can't see how this is possible so I thought I'd see if anyone else has any ideas. Some form of system-wide SetDllDirectory call would help or some registry hack that could set the working directory when a 3rd-party app calls LoadLibrary on my plugin.
IMO separating the COM object into a separate .dll is the cleanest solution - anyone would expect an in-proc COM server to be registered by using regsvr32 and that requires no fancy dependencies in that COM server.
I don't know if it's precisely a solution to your problem, but maybe this can help you: try to look at the possibilities offered by manifest files. I hope it will help.
You could use a runtime registration model.
The Dll could register itself as a COM server in its own initialisation code.
This only requires that loadlibrary is guaranteed to be called before the dll is used as a COM server.
Related
My basic issue is this: my program (MyProgram.exe) has a dependency on a DLL from another program (OtherProgram), and I'm trying to avoid repackaging a new DLL every time OtherProgram updates. I'd like to have MyProgram.exe link in OtherProgram's DLL when it launches, but I'm not completely sure that Windows allows for this. So if there is some kind of workaround that would also be acceptable.
And just for some background, the platform is Windows 7 x64, and MyProgram.exe runs fine when I create a symlink in the MyProgram.exe project directory to the DLL in OtherProgram's install directory. When I try to run it without the symlink, I get the "program can't start because OtherProgramDLL.dll is missing from your computer" error.
Any advice or links to relevant info is greatly appreciated!
EDIT: Clarification: the DLL is not linked at compile-time, this issue crops up at runtime
There are two types of dynamic linking in the Windows world:
Load-Time linking is when a DLL is loaded automatically when your program starts up. Windows finds this DLL using a specific algorithm I'll discuss below.
Run-Time linking is when you specifically load a DLL by calling LoadLibrary in your code. Similar rules apply as to how the library is found, but you can specify a fully-qualified or relatively-qualified path to control the search.
In the case of Load-Time linking, MS recommends that your program's DLLs are stored in and loaded from the same directory where your application is loaded from. If this is at all workable, this is probably your best option.
If that doesn't work, there are several other options, outlined here. One is to leverage the search order by putting the DLL in either the working directory or the directory where the application was loaded from.
You can change the working directory of an application by:
Create a shortcut to your application.
Bring up the shortcut's properties
Edit the "Start in" property with the directory where the DLL is located.
When you launch your application using the shortcut, it will load the right DLL.
Other options for load-time linking include:
Adding a manifest to your application which specifies where your dependent assemblies are, or,
Setting the PATH.
You could use LoadLibrary, but you would need a way to guarantee the DLL's location. This Wikipedia article provides good example on how to use the DLL after it has been loaded.
You can add the directory where the dll is located to the PATH environment variable.
I have struggled with the same problem and also found a dead end with the suggested methods like LoadLibrary, SetDllDirectory, Qt's addLibraryPath and others. Regardless of what I tried, the problem still remained that the application checked the libraries (and didn't find them) before actually running the code, so any code solution was bound to fail.
I almost got desperate, but then discovered an extremely easy approach which might also be helpful in cases like yours: Use a batch file! (or a similar loader before the actual application)
A Windows batch file for such a purpose could look like this:
#echo off
PATH=%PATH%;<PATH_TO_YOUR_LIB>
<PATH_TO_YOUR_APP_EXE>
/edit: Just saw #SirDarius comment in Luchian's answer which describes that way, so just take my batch code bit as a reference and all credits go to him.
I have the same problem with one application I am working on.
I do not want to use runtime loading because there are tens of functions I would need to manually create function pointer for.
Mr Dibling's mention of manifest file opened a new door for me but I sadly found out that the oldest version of windows that supports the feature is Windows 7. It won't even work on Vista.
Long story short, a friend familiar with Windows Application development told me to look up Delay-Loaded DLL, which turns out to solve the problem perfectly with minimal effort. It delays the loading of DLL library to either the point you manually do, or the first time its function is called. So you just need to add your DLL path to the search path before that happens, where SetDllDirectory helps.
Here is the steps to make it work:
1) Specify the DLL to be delay-loaded to linker, either through your makefile, cmake or VS property page (Linker->Input of VS2015)
2) Call SetDllDirectory at the beginning of your program, before any call to the DLL is made.
Delay-loaded DLL is supported all the way back to VC6.
SetDllDirectory is supported after XP SP1.
Use Symbolic Links to the 3rd Party Executables
I found the approach advocated by Aaron Margosis useful. See:
Using NTFS Junctions to Fix Application Compatibility Issues on 64-bit Editions of Windows
Essentially, create symbolic links to each of the dependent 3rd Party executables. Place these symbolic link files in and amongst your own dependent executable files. Except for filename changes to the targets, the 'soft' symbolic links will resolve the load-time dependencies even as the target of the links are changed by future updates.
My application uses one version of library (a.dll), I am using another DLL(b.dll) which in-turn uses older version of the same library (a.dll) that i use. I am building the application by embedding a manifest file. The DLL i use is also using a embedded manifest file. I am having both the versions of the library in my WinSXS folder. My application is not able to load the appropriate versions of DLLs.
Will having a separate manifest file (not embedding into DLL) help resolving the problem? What is the work around?
Your situation is exactly the situation WinSxS is supposed to solve. It should be working.
Either: The manifest files are pointing to the same version, or one of the manifest files is not embedded properly, or
The shared assembly in WinSxS was installed with a configuration policy that automatically redirects requests for v1.0 to v1.1
Some clarifications are needed: App.exe and b.dll are implicitly linked against a.dll? Or do they load it via LoadLibrary.
If B.DLL loads A.DLL explicitly using LoadLibrary then you need to add ISOLATION_AWARE_ENABLED to your pre-processor definitions to ensure that LoadLibrary calls made by B.DLL look in the correct activation context. Otherwise they will be made in the context of the default activation context which was created by the EXE's manifest.
It will depend on what the duplicated DLLs do and if their versions are compatible. (e.g. Do they both access shared objects in memory? If so, there's a good chance something will blow up.)
It will also depend on how those two same-named DLLs are loaded. If it's anything other than an explicit LoadLibrary with a full path then things probably will not work. There's an ongoing discussion of this here: Determine the loaded path for DLLs
In general, it might work if you're lucky. The fact it may go catastrophically wrong is a good reason to avoid the issue entirely, if you can. (In the worst case, you could host one of the modules in another process and proxy all the calls to it. Ideally, just be able to use the same DLL version in both modules.)
I have a COM dll that is working fine as an in-proc server and I install it in Component Services COM+ Applications. Now when I try to CoCreate it from my client app, I get HRESULT 0x8007007e "The specified module could not be found". What could be causing this?
Module not found means that the COM system tried to load a module/dll (probably referred to by a GUID) that wasn't found, either because it wasn't registered, or because the dll was not present at the registered path.
I used to get this error when trying to create an object "A" from e.g. A.dll, which called into another dll (B.dll) that wasn't registered.
A tool you may be interested in is process monitor, which tells you exactly what register keys were looked for by what process, with failure and success codes, and even let you see it's call stack.
Please elaborate on the different circumstances between working and not working.
I suspect there is a module that is depended on that is not found - some dll that is not in a search path for example.
HArd to tell . I rember that usually I need to register com component with something like that:
Regsvr32 my_com.dll
Also you may verify that the path to your DLL is in PATH envornnemnt variable (Is it PATH or another variable?). Or copy it in the folder for your application.
Verify also your user's rights on this DLL.
The dll was registered on a ClearCase dynamic view, similar to a mapped drive, not available to COM+. Solution was to move the dll and the proxy/stub dll to a local drive and register them there.
I've added a new library to my application (multiple projects-DLLs) - SQLite, to perform some in memory caching. There is just one library/project that is affected by this change - Lib1.
A build goes through fine. All libraries are built successfully and no errors are reported, including a couple of Com Objects.
If I try to register the com objects, I get the The DLL could not be loaded. Check to make sure all required application runtime files and other dependent DLLs are available in the component DLL's directory or the system path. message. But all the libs are at the same place. And all are in the path. A copy of this project builds and registers fine (without the few changes made for SqlLite ofcourse). Dependency walker reports no issues
Oddly, if I try to register the DLL of the com object (using regsvr32) it works fine. Also, I have another library, which is dependant on Lib1 (not on SqlLite) which also cannot be loaded.
Any ideas?
Thanks,
A'z
You can use Process Monitor (http://technet.microsoft.com/en-us/sysinternals/bb896645.aspx) set to filter process name regsvr32.exe in order to see all file and registry access.
Always use full path to your-com-dll when you issue regsvr32 commands, if you have the same dll somewhere else in path (for example c:\windows\system32) regsvr32 will use the other dll and not the one in your current directory.
Another trick would be to use "rundll32 your-com-dll,DllRegisterServer". In case of missing dlls it will tell which dll is missing instead of just saying that LoadLibrary failed.
Edit:
What do you mean by "If I try to register the com objects"? How are you doing this? I'm asking because you say that regsvr32 on the dll which actually implements these com object works fine.
Use the dependency walker tool to figure out what other dlls the COM server relies on. Then check the executable paths that is set in Visual Studio (Tools -> Options -> Projects -> Directories (I think)). Note that VS does not use the system PATH environment variable - it uses what is set in the options page so if the path to the dependencies is not listed there, the registration would fail, even though if you used regsvr32 from the command line it would succeed.
And so, the plot thickens!!!!
I've actually narrowed down the to the line of code that causes this linking problem.
In the modified library (LIB1) I've added a new class A1 which inherits from an existing class A.
When I change an existing class B which used to inherit from A to now inherit from A1 - this is when the problem is caused. Class B is in a lib3.
I've verified that just when I change the inheritance, only then the problem occurs!!!
I've used file-mon on regsvr32 when loading successfully and when failing. I stuggle to find the difference! Tomorrow morning I'll try Process Monitor and see if it helps.
Still desperate for help,
A'z
hmm... as Christian asks, how else are you attempting to register the objects if regsvr32.exe succeeds?
the rundll32.exe advice is also good. have you tried stepping through DllRegisterServer in a debugger to see precisely when it's failing? this sounds like a potential runtime failure if depends.exe isn't revealing anything.
btw, when i google for that exact error text i see: http://social.msdn.microsoft.com/forums/en-US/sqldataaccess/thread/402c1767-cf1d-42f0-aec9-e0169dbf1083/, but I assume you've probably already done this search and found it not helpful :)
I am writing a DLL to plug into another (3rd party) application. The DLL will need to depend on another set of DLLs (for license reasons I cannot link statically).
I would like my DLL to be "xcopy-deployable" to any directory. I would also like not to require adding this directory to the path.
If I just build the DLL the usual way, Windows will refuse to load the DLL, since it cannot find the DLLs next to the current process.
Are there any good options for helping Windows locate the DLL?
To answer some questions:
The DLL is written in C++.
The extra DLLs are QT-dlls.
I would like to place the extra DLLs in the same folder as my plugin DLL. I can get the name of that folder from GetModuleFileName.
The application is Firefox, the DLL is a PKCS#11 security module.
The application loads the DLL using the full path to the DLL (the user supplies it when installing the plugin).
Requiring that the DLLs be placed in System32 or next to the application would work, but it is a bit messy and could cause problems with uninstallers.
LoadLibrary and GetProcAddress would of course work, but is not really feasible in my case. I am using hundreds, if not thousands, of methods in the other DLLs. I really need to use the import-libraries.
I had thought about using delay-loaded dlls combined with SetDllDirectory in DllMain. Have anyone tried anything like this?
I can think of 3 ways.
put the dlls in the same folder as your application (you cannot do this?)
Use runtime linking. LoadLibrary() and GetProcAddress()
Use a manifest http://msdn.microsoft.com/en-us/library/aa374182(VS.85).aspx
But if the dll isn't in the same folder as the .exe, how are you going to know where it is? forget Windows not knowing, how do you know?
you can specify the path of dll as the parameter of LoadLibrary().
Another option is to modify the PATH variable. Have a batch file for launching the main app, and set the PATH=%PATH%;%~dp0. This ensures a minimal footprint, with no additional traces left in the system after running.