32-bit to 64-bit : LNK2019 error, how to retrieve relevant information

Question

I'm working on a 32-bit C++ application, which I'm converting to a 64-bit application (simply choose another configuration, copy and adapt all relevant settings, and try to get it to build), and now I get stuck on linker error LNK2019 "unresolved external symbol ... referenced in function ...", and I'd like to get more information:
I have already re-built the application in 32-bit, and I've found the referred function, but when I press F12, Shift+F12 or Ctrl+F12 I don't see where the implementation is retrieved from.

I think that the function's implementation is somewhere inside a DLL, but I want to be sure of it (once this is confirmed, I can look for the corresponding settings, defining the location, and copy this setting for my 64-bit configuration).

Maybe the question can be reformulated in the following way: in case a function is retrieved from a DLL, is it possible to know in which DLL this function is implemented?

You could look at the assembly language for the program and see where it calls out to. Or run the program and F11 into the function to see where it goes. — Raymond Chen, May 30 '18 at 13:23
Having the linker produce a .map file in the 32-bit build would be the simplest way to find it. — Hans Passant, May 30 '18 at 13:34
@RaymondChen the errors are from a linker issue. So it cannot be debugged. — Robert Andrzejuk, May 30 '18 at 14:11
Debug the 32-bit version that works. My guess it's in a library that you haven't converted to 64-bit. — Raymond Chen, May 30 '18 at 14:41

score 0 · Accepted Answer · answered May 31 '18 at 09:11

Hans, the advise about the *.map file was a life saver: this allowed me to know in which file the mentioned function was to be found.
Obviously, that was not the end of it: the mentioned file was a DLL, while there is no reference towards the DLL itself, but towards a LIB file, who redirects towards the DLL.
In case this is not difficult enough: the function itself was a __imp_ function, and there seems to be a catch there:

32-bit : __imp__ functions (watch both underscores after imp)
64-bit : __imp_ functions (watch the single underscore after imp)

Finally I solved the issue by checking the build output (compare LIB= and PATH= entries and make sure they are similar for both cases: when there is a reference to the 32-bit libraries in one output, there should be a reference to the 64-bit libraries in the other output).
In the 32-bit output, I saw that the linker was referring to a lib, which he did not do in case of the 64-bit linking: I added the corresponding lib in the project's configuration (Configuration properties, Linker, Input, Additional Dependencies), and this finally solved the issue.

32-bit to 64-bit : LNK2019 error, how to retrieve relevant information

1 Answers1