Curious about dumpbin output

[John E]

About 3 years ago I compiled a DLL containing a library of audio processors called Vamp plugins. Three years later, a few more plugins have been added to the library so yesterday, I decided to rebuild it. Unfortunately, the new build doesn't seem to be working

Before I dig too deeply.. there's an obvious difference if I run dumpbin /EXPORTS on the built lib. Here's the older build (note the highlighted line)

Microsoft (R) COFF/PE Dumper Version 8.00.50727.762
Copyright (C) Microsoft Corporation.  All rights reserved.

Dump of file libardourvampplugins.dll

File Type: DLL

  Section contains the following exports for libardourvampplugins.dll

    00000000 characteristics
    53536D48 time date stamp Sun Apr 20 07:46:32 2014
        0.00 version
           1 ordinal base
           1 number of functions
           1 number of names

    ordinal hint RVA      name

          1    0 0000E540 vampGetPluginDescriptor = _vampGetPluginDescriptor

  Summary

        1000 .data
        5000 .rdata
        2000 .reloc
        1000 .rsrc
       14000 .text

and here's the version from yesterday...

Microsoft (R) COFF/PE Dumper Version 8.00.50727.762
Copyright (C) Microsoft Corporation.  All rights reserved.

Dump of file libardourvampplugins.dll

File Type: DLL

  Section contains the following exports for libardourvampplugins.dll

    00000000 characteristics
    5899905A time date stamp Tue Feb 07 09:16:10 2017
        0.00 version
           1 ordinal base
           1 number of functions
           1 number of names

    ordinal hint RVA      name

          1    0 00001BA9 vampGetPluginDescriptor

  Summary

        2000 .data
        3000 .idata
       13000 .rdata
        5000 .reloc
        1000 .rsrc
       81000 .text

Does that difference signify something?? Both were built using MSVC 8 and I used the same version of dumpbin in both cases..

[2kaud]

I think that the LHS name is the exported name and the RHS name is the internal name. From the code, is the name VampGet or _VampGet?

[John E]

I think that the LHS name is the exported name and the RHS name is the internal name. From the code, is the name VampGet or _VampGet?

Hi 2kaud. The name is "vampGetPluginDescriptor" (without an underscore). But IIRC an underscore indicates that the function got exported with 'C' linkage. C++ functions normally have some name mangling stuff (except that this one happens to be in global scope so there's no classname or namespace etc). Here's what I see if I build a Debug version:

Microsoft (R) COFF/PE Dumper Version 8.00.50727.762
Copyright (C) Microsoft Corporation.  All rights reserved.

Dump of file libardourvampplugins.dll

File Type: DLL

  Section contains the following exports for libardourvampplugins.dll

    00000000 characteristics
    589AFF64 time date stamp Wed Feb 08 11:22:12 2017
        0.00 version
           1 ordinal base
           1 number of functions
           1 number of names

    ordinal hint RVA      name

          1    0 00001974 vampGetPluginDescriptor = @ILT+2415(_vampGetPluginDescriptor)

  Summary

        2000 .data
        3000 .idata
       2A000 .rdata
        7000 .reloc
        1000 .rsrc
       AC000 .text

I'm guessing that the Release build is exporting the function as C++ somehow

[2kaud]

To stop the name mangling and export as c, you use extern "c" {...} around the import/export. See
https://msdn.microsoft.com/en-us/library/ys435b3s.aspx
https://msdn.microsoft.com/en-us/library/wf2w9f6x.aspx

PS Does the project use a .def file?

[John E]

PS Does the project use a .def file?

Yes, it looks like this:

; Auto-generated by create_symbols_file.py

LIBRARY libardourvampplugins.dll
EXPORTS

vampGetPluginDescriptor           @1

I just noticed that the function is in a file with the extension .cpp. So my guess is that I was previously compiling it as 'C' code but now I'm compiling as C++.