Changes in the DLL Delayed Loading Helper Function Since Visual C++ 6.0
The latest version of this topic can be found at 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
Note
If you are using the default helper function, these changes will not affect you. There are no changes regarding how you invoke the linker.
Multiple Versions of Visual C++
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.
User-Defined Helper Function
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.
Load All Imports for a Delay-Loaded DLL
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.