2 decorated names with same entry point

Question

Hello,

Is there any way to have 2 decorated names for the same entry point of a C function for a DLL created with MSVC?

For example:

void __declspec(dllexport) foo(void);

So the DLL exports the function foo for entry point 0x00001000 and _foo on this same entry point ?

I ask because I saw a dll with this kind of double naming of decorated names for backwards compatibility issues

Greetings

Answer 1

One way is to use a .def file to create an alias.

Answer 2

I found a workaround by compiling as C++ instead of C.

C:\Users\RLWA32\source\repos\Rlwa32\FooLib\FooLib>cl /c /MD /Tp FOOBar.c  
Microsoft (R) C/C++ Optimizing Compiler Version 19.29.30143 for x86  
Copyright (C) Microsoft Corporation.  All rights reserved.  
  
FOOBar.c  
  
C:\Users\RLWA32\source\repos\Rlwa32\FooLib\FooLib>lib /out:mylib.lib FOOBar.obj  
Microsoft (R) Library Manager Version 14.29.30143.0  
Copyright (C) Microsoft Corporation.  All rights reserved.  
  
  
C:\Users\RLWA32\source\repos\Rlwa32\FooLib\FooLib>link /map /mapinfo:exports /def:FooLib.def /machine:x86 /DLL /out:FooLib.dll mylib.lib msvcrt.lib  
Microsoft (R) Incremental Linker Version 14.29.30143.0  
Copyright (C) Microsoft Corporation.  All rights reserved.  
  
LINK : warning LNK4001: no object files specified; libraries used  
   Creating library FooLib.lib and object FooLib.exp  
  
C:\Users\RLWA32\source\repos\Rlwa32\FooLib\FooLib>dumpbin /exports FooLib.dll  
Microsoft (R) COFF/PE Dumper Version 14.29.30143.0  
Copyright (C) Microsoft Corporation.  All rights reserved.  
  
  
Dump of file FooLib.dll  
  
File Type: DLL  
  
  Section contains the following exports for FooLib.dll  
  
    00000000 characteristics  
    FFFFFFFF time date stamp  
        0.00 version  
           1 ordinal base  
           2 number of functions  
           2 number of names  
  
    ordinal hint RVA      name  
  
          1    0 00001C90 FOOBar  
          2    1 00001C90 _FOOBar  
  
  Summary  
  
        1000 .data  
        1000 .rdata  
        1000 .reloc  
        1000 .text  
  
C:\Users\RLWA32\source\repos\Rlwa32\FooLib\FooLib>  

FOOBar.c

#include "framework.h"  
  
void FOOBar(void)  
{  
    OutputDebugStringW(L"Function body for FOOBar\n");  
}  

Header -

#pragma once  
  
#define WIN32_LEAN_AND_MEAN             // Exclude rarely-used stuff from Windows headers  
// Windows Header Files  
#include <windows.h>  
  
  
__declspec(dllexport) void FOOBar(void);  

FooLib.def -

LIBRARY  
  EXPORTS  
    _FOOBar=?FOOBar@@YAXXZ  
    FOOBar=?FOOBar@@YAXXZ  

Linker map -

 Exports  
  
  ordinal    name  
  
        1    ?FOOBar@@YAXXZ (void __cdecl FOOBar(void))  
               exported name: FOOBar  
        2    ?FOOBar@@YAXXZ (void __cdecl FOOBar(void))  
               exported name: _FOOBar  




  

Answer 3

Thank you very much. I have created a POC to verify this and yes, it does work.
The problem is that my project uses additional options in our (complex) build process that disrupts this part.

Answer 4

I tried to replicate your environment from the command line. Both function names were exported -

C:\Users\RLWA32\source\repos\Rlwa32\FooLib\FooLib>cl /c foo.c
Microsoft (R) C/C++ Optimizing Compiler Version 19.29.30143 for x86
Copyright (C) Microsoft Corporation.  All rights reserved.

foo.c

C:\Users\RLWA32\source\repos\Rlwa32\FooLib\FooLib>lib /out:mylib.lib foo.obj
Microsoft (R) Library Manager Version 14.29.30143.0
Copyright (C) Microsoft Corporation.  All rights reserved.


C:\Users\RLWA32\source\repos\Rlwa32\FooLib\FooLib>link /map /mapinfo:EXPORTS /def:FooLib.def /machine:x86 /DLL /out:FooLib.dll mylib.lib
Microsoft (R) Incremental Linker Version 14.29.30143.0
Copyright (C) Microsoft Corporation.  All rights reserved.

LINK : warning LNK4001: no object files specified; libraries used
   Creating library FooLib.lib and object FooLib.exp

C:\Users\RLWA32\source\repos\Rlwa32\FooLib\FooLib>dumpbin /exports FooLib.dll
Microsoft (R) COFF/PE Dumper Version 14.29.30143.0
Copyright (C) Microsoft Corporation.  All rights reserved.


Dump of file FooLib.dll

File Type: DLL

  Section contains the following exports for FooLib.dll

    00000000 characteristics
    FFFFFFFF time date stamp
        0.00 version
           1 ordinal base
           2 number of functions
           2 number of names

    ordinal hint RVA      name

          1    0 00001000 _foo
          2    1 00001000 foo

  Summary

        2000 .data
        6000 .rdata
        1000 .reloc
        A000 .text

C:\Users\RLWA32\source\repos\Rlwa32\FooLib\FooLib>

And from the linker map -

 Exports

  ordinal    name

        1    _foo
        2    _foo
               exported name: foo