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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
One way is to use a .def file to create an alias.
I tried, however it does not work when I use a "DEF" file. The exported symbol is not "foo" but "_foo" when I want both.
One thing I left out in my original post is that I generate the DLL from a static lib.
DEF file -
LIBRARY
EXPORTS
_foo = foo
foo = foo
Linker map showing exports -
Exports
ordinal name
1 _foo
2 _foo
exported name: foo
And output of dumpbin.exe showing both exports
I have isolated the issue:
il you create a function like this:
void __declspec(dllexport) FOOBar(void);
Then export ignore alias with underscore is ignored
![](data:image/svg+xml, %3Csvg xmlns='http://www.w3.org/2000/svg' height='64' class='font-weight-bold' style='font: 600 30.11764705882353px "SegoeUI", Arial' width='64'%3E%3Ccircle fill='hsl(179.20000000000002, 34%, 27%)' cx='32' cy='32' r='32' /%3E%3Ctext x='50%25' y='55%25' dominant-baseline='middle' text-anchor='middle' fill='%23FFF' %3EXY%3C/text%3E%3C/svg%3E)
Anyway you can write another function which calls the origin function.
Following header was included in the creation of FooLib.dll from which above was generated -
#pragma once
#define WIN32_LEAN_AND_MEAN // Exclude rarely-used stuff from Windows headers
// Windows Header Files
#include <windows.h>
extern "C" void __declspec(dllexport) foo(void);
I tried, it did not change anything. Here are the sources of my POC, close to our construction system allowing to reproduce my problem.
api.h:
#ifndef __API_H
#define __API_H
#ifdef __GNUC__
#define DEPRECATED __attribute__((deprecated))
#else
#define DEPRECATED __declspec(deprecated)
#endif
# ifdef __API_IMPLEMENTATION
# ifdef __GNUC__
# define API __attribute__((visibility ("default")))
# else
# define API __declspec(dllexport)
# endif
# else
# define API extern
# endif
#endif
module.h
#include "api.h"
API void FOOBar(void);
module.c
#include <stdio.h>
#include "module.h"
API void FOOBar(void)
{
printf("%s\n", __FUNCTION__);
}
version.c
static const char VERSION[] = "FOO 1.0";
export.def:
EXPORTS
FOOBar = FOOBar
_FOOBar = FOOBar
And commands line close to our build process:
cl /c /TC /D__API_IMPLEMENTATION=1 /DWIN32_LEAN_AND_MEAN=1 module.c version.c
lib /OUT:myLib.lib module.obj
link /MAP /DEF:export.def /MACHINE:X86 /DLL /OUT:theLib.dll version.obj myLib.lib
I get this result:
regards
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
@CG85 Any updates?
Thanks for your comment, this workaround works for this POC :)
Unfortunately, I can't switch from C to C++ due to compile-time side effects (multiple errors that I can't fix for various reasons).
Although I have answered your question two different ways I'm sorry to hear that neither answer works for you in your particular circumstances.
I thank you for the time you spent to help me, it allowed me to advance my problem :)
On the other hand, I am very curious to know the difference of treatment between C and C++ made by MSVC, contrary to GCC where I have no problem.
Is there a doc not listed on MSVN about this ?
Anyway, thanks for everything!
MSVC is a compiler that is now incorporated into visual studio. By default, the Visual C++ compiler treats all files that end in .c as C source code, and all files that end in .cpp as C++ source code. To force the compiler to treat all files as C regardless of file name extension, use the /Tc compiler option.
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.
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
with "foo" function name yes, it works.
But if your function is named "FOOBar" (uppercase prefix) like in my sample code , you may reproduce the issue.
Issue reproduced with FOOBar. Potential workaround posted below to avoid 1600 character limitation in comments.