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Changes in the DLL Delayed Loading Helper Function Since Visual C++ 6.0

If you have multiple versions of Visual C++ on your computer or if you defined your own helper function, you may be affected by changes made to the DLL delayed loading helper function. For example:

  • __delayLoadHelper is now __delayLoadHelper2

  • __pfnDliNotifyHook is now __pfnDliNotifyHook2

  • __pfnDliFailureHook is now __pfnDliFailureHook2

  • __FUnloadDelayLoadedDLL is now __FUnloadDelayLoadedDLL2


If you are using the default helper function, these changes will not affect you. There are no changes regarding how you invoke the linker.

If you have multiple versions of Visual C++ on your computer, make sure the linker matches delayimp.lib. If there is a mismatch, you will get a linker error reporting either ___delayLoadHelper2@8 or ___delayLoadHelper@8 as an unresolved external symbol. The former implies a new linker with an old delayimp.lib, and the latter implies an old linker with a new delayimp.lib.

If you get an unresolved linker error, run dumpbin /linkermember:1 on the delayimp.lib that you expect to contain the helper function to see which helper function is defined instead. The helper function could also be defined in an object file; run dumpbin /symbols and look for delayLoadHelper(2).

If you know you have the Visual C++ 6.0 linker, then:

  • Run dumpbin on the delay load helper's .lib or .obj file to determine whether it defines __delayLoadHelper2. If not, the link will fail.

  • Define __delayLoadHelper in the delay load helper's .lib or .obj file.

If you defined your own helper function and are using the current version of Visual C++, do the following:

  • Rename the helper function to __delayLoadHelper2.

  • Since the pointers in the delay descriptor (ImgDelayDescr in delayimp.h) have been changed from absolute addresses (VAs) to relative addresses (RVAs) to work as expected in both 32- and 64-bit programs, you need to convert these back to pointers. A new function has been introduced: PFromRva, found in delayhlp.cpp. You can use this function on each of the fields in the descriptor to convert them back to either 32- or 64-bit pointers. The default delay load helper function continues to be a good template to use as an example.

The linker can load all imports from a DLL that you specified to be delay loaded. See Loading All Imports for a Delay-Loaded DLL for more information.

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