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c++winapidlluwp

What are "api-ms-win-*-*-lx-x-x.dll" umbrella libraries?

I keep running into DLLs with long file names, as such. Just two for example: "api-ms-win-appmodel-runtime-l1-1-1.dll" or "api-ms-win-appmodel-identity-l1-2-0.dll". Evidently Microsoft calls them "umbrella libraries".

My original understanding was that they were just new DLLs with new file names, but then I tried to search for those files. Well, I couldn't find them as physical files on disk ...

So I'm curious, are they some sort of virtual DLL file names that don't exist on disk?

WCHAR buff[MAX_PATH];
buff[0] = 0;
GetSystemDirectory(buff, MAX_PATH);
StringCchCat(buff, MAX_PATH, L"\\api-ms-win-appmodel-runtime-l1-1-1.dll");

HMODULE hModule = LoadLibrary(buff);
//'hModule' is NULL & error code is ERROR_MOD_NOT_FOUND

But the following works:

HMODULE hModule = LoadLibrary(L"api-ms-win-appmodel-runtime-l1-1-1.dll");
Solution

  • These are “Virtual DLL” names. When we call LoadLibrary, the Windows loader (e.g., LdrLoadDll) will check for well known name prefixes (ex. api-) and if the name begins with one of these - it will use the ApiSetSchema mechanism to translate the virtual dll name (i.e api-ms-win.. ) to the real dll name (e.g., a file name, like kernel32.dll, kernelbase.dll, etc). this mapping is implemented in ApiSetSchema.dll which is located in the system32 folder.

    enter image description here

    Regarding the internal implementation - read Runtime DLL name resolution: ApiSetSchema - Part II and The API Set Schema.

    You may also reference Microsoft's original documentation for API Set Schemas, US patent publication "US 2014/0366045 A1", which covers the original motivations for the technology and the overarching design that Microsoft implemented.