LoadLibrary Module Not Found - DLL Hell After Offi

问题:

Unfortunately this is going to be a pretty open-ended question, but I am at my wit's ends and I thought I would reach out for some advice.

This is a Visual C++ MFC app using Visual Studio 2008 SP1.

A coworker and I both had Office 2007 installed and we have both had strange DLL loading problems with our app since. Specifically, LoadLibrary is failing to load one our DLLs ( the first one it loads ) and returning error code 126 ( module not found ). What's really strange is that if I just run the executable from the windows explorer it works fine.

I took the usual steps to diagnose the problems:

1. Verify that the file existed and that the current working directory was pointed at it.
2. Run dependency walker and verify that it's dependencies are loading correctly. They are all loading ok except the ones this question says are ok to fail.
3. Experiment with loading some different DLLs at the same location in the code. Some of the simple 'stub' dlls succeed, but most of them fail.
4. Experiment with loading the DLLs that are failing from separate test apps - in an empty console app and a barebone MFC app, all the DLLs are loading fine!
5. Try to load the DLLs with LoadLibraryEx and the LOAD_LIBRARY_AS_DATAFILE flag, which does succeed but doesn't get us very far except to point out it's probably a dependency problem.

I really don't know what else to do at this point. Like I said, Office 2007 is a common thread in our problem but I don't know what kind of problems it could create. I really don't know even what steps to take next. Any ideas?

edit: I'm pretty sure the current working directory is not in the DLL path for some reason. It seems the DLLs that are failing are ones that need any other DLLs. If I turn on Loader Snaps debug output the current working directory does not appear to be in the DLL loading path. Any idea what could cause this?

edit2: The current build dumped the executable into a directory other than the working directory. For some reason, when I tried to load a DLL which then tried to load ANOTHER DLL, the current working directory is no longer searched. By putting the executable into the directory with all of the DLLs I am trying to load, the problems go away. Based on all of this, and the output by loader snaps, I am 98% sure this is some bizarre Visual Studio bug and I will simply have to work around it.

回答1:

Office 2007 turns on SafeDllSearchMode in the registry.

http://msdn.microsoft.com/en-us/library/ms682586%28VS.85%29.aspx

With SafeDlLSearchMode, the current directory is no longer searched. To disable it, they claim you can go into regedit and set HKLM/System/CurrentControlSet/Control/SessionManager/SafeDllSearchMode to 0, but this did not work for me. Calling SetDllDirectory to the current directory DID work for me, although this only works if you are targeting XP SP1+.

The reason this caused problems in my specific app is that when we run the executable from the debugger, we keep the executable in a different directory than the current directory with all the other build files. When we run outside of Visual Studio, we first copy the executable into the directory with all of the other DLLs. The directory that the original executable is called from is ALWAYS in the search path, so if you keep your executable and your dlls together, you would never run into this problem.

Still, it's quite confusing for Microsoft to change the dll search path under us like this.

回答2:

Does the DLL which fails has MSVCRT80 in dependencies? If yes, the most likely reason is that Office 2007 has overridden MSVCR80.dll