Instead, they are defined in the application manifest: when the COM loader finds an entry in the manifest for the specified GUID, it loads the corresponding DLL and doesnt apply the default registry loading routine.France Follow me on Twitter 36 posts 26 tags Highway to (DLL) Hell 2018-10-07 Development Its no secret that Ive always been a huge fan of Windows Media Center, probably the best digitalpersonal video recorder out there and definitely one of the most impressive Microsoft applications developed using the.NET Framework.As an avid WMC user, I have built 3 HTPC machines and recorded thousands of TV programs (movies, series, documentaries, etc.).
Manifest Tool Mt Windows 10 I RefusedAs such, when Microsoft announced in May 2015 that Windows Media Center would no longer be developed (almost 6 year after disbanding the development team) and thus would not be part of Windows 10 I refused to migrate to Windows 10, despite Microsofts offers encouraging users to upgrade their OS for free.
The fact Windows Media Center was not available on Windows 10 even as a paid feature like it was on Windows 8.x was a major blocker for many users. To work around this limitation, enthusiasts decided to create an unofficial port of Windows Media Center for Windows 10. Manifest Tool Mt Update Some OfBut over time, Microsoft started to update some of the system components Windows Media Center relied on, causing annoying bugs. Manifest Tool Mt Windows 7 Completely ImpossibleFor instance, the introduction of breaking changes in Windows 10 1803 made watching a.wtv file (WMCs TV file format) recorded on Windows 7 completely impossible. While investigating, I discovered that the issue was caused by a change in MSVidCtl.dll, the system-wide DLL containing the DirectShow components needed by WMC for all its TV-related features. After replacing the faulty DLL by an older version, WMC was able to play old recordings like a charm. This phenomenom, that occurs every time API or functional changes are introduced in a DLL a program depends on, has a name: DLL Hell. You shall not replace system DLLs The thing is, replacing a system-owned DLL is far from ideal: while it solves the initial problem quite easily, its not future-proof as any major Windows update will end up overwriting the replaced DLL. It may also cause issues in other applications depending on new APIs that are only part of the newest version of the replaced DLL. Since replacing a system DLL was not a good option, I eventually opted for the other approach: forcing Windows Media Center to load its own version of MSVidCtl.dll instead of the global one stored in System32. Typically, youd achieve that by simply dropping the DLL in the applications root folder (in our case, C:Windowsehome ). This usually works because the DLL loader first looks for the DLL in the directory the application was loaded from. Enter the marvelous world of COM In this case, this didnt work: Windows Media Center kept loading the MSVidCtl DLL contained in the System32 folder. Why Because MSVidCtl.dll is actually a very special DLL: its a Component Object Model DLL. Unlike other DLLs, COM DLLs are almost never loaded via LoadLibrary (at least, not directly): instead, they are assigned a GUID that corresponds to a special entry in the registry that contains the absolute path of the COM DLL. When an application wants to instantiate a COM component, it usually imports Ole32.dll and calls CoCreateInstance with the unique GUID: the COM loader locates the entry in the registry and loads the DLL from the associated path. Since the path is absolute, trying to add a MSVidCtl.dll in the ehome folder was completely pointless: the loader would never look for it. DLL redirection and side-by-side assemblies To mitigate this issue, Microsoft offers 2 mechanisms that allow overriding the default search order used by Windows DLL loader even when the specified path is absolute: DLL redirection: by creating an empty.local filefolder whose name is the same as the executable (in our case, ehshell.exe.local ), one can easily force the OS to load DLLs from the application folder: its dead simple and works flawlessly, even for COM DLLs. Unfortunately, it has a major caveat: it doesnt work when the application has an application manifest (theres a registry switch to override that but turning it on would impact the entire system, certainly not a good thing to do). Side-by-side assemblies: first introduced in Windows 98 Second Edition, it allows an application to define its dependencies in its application manifest (and explicitly opt for a specific DLL version). DLL dependencies can be either stored in the same directory as the application (in this case, they are known as private assemblies) or in a special shared directory called winsxs. Starting with Windows XP, it also allows defining registration-free COM components: unlike classical COM components, they dont have an entry in the registry and thus are not registered globally.
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