Export all symbols when creating a DLL

Short answer

You can do it with help of the new version of the CMake (any version cmake-3.3.20150721-g9cd2f-win32-x86.exe or higher).

Currently it's in the dev branch.Later, the feature will be added in the release version of the cmake-3.4.

Link to the cmake dev:

cmake_dev

Link to an article which describe the technic:

Create dlls on Windows without declspec() using new CMake export all feature

Link to an example project:

cmake_windows_export_all_symbols

Long answer

Caution:All information below is related to the MSVC compiler or Visual Studio.

If you use other compilers like gcc on Linux or MinGW gcc compiler on Windows you don't have linking errors due to not exported symbols, because gcc compiler export all symbols in a dynamic library (dll) by default instead of MSVC or Intel windows compilers.

In windows you have to explicitly export symbol from a dll.

More info about this is provided by links:

Exporting from a DLL

HowTo: Export C++ classes from a DLL

So if you want to export all symbols from dll with MSVC (Visual Studio compiler) you have two options:

• Use the keyword __declspec(dllexport) in the class/function's definition.
• Create a module definition (.def) file and use the .def file when building the DLL.

1. Use the keyword __declspec(dllexport) in the class/function's definition

1.1. Add "__declspec(dllexport) / __declspec(dllimport)" macros to a class or method you want to use. So if you want to export all classes you should add this macros to all of them

More info about this is provided by link:

Exporting from a DLL Using __declspec(dllexport)

Example of usage (replace "Project" by real project name):

// ProjectExport.h#ifndef __PROJECT_EXPORT_H#define __PROJECT_EXPORT_H#ifdef USEPROJECTLIBRARY#ifdef  PROJECTLIBRARY_EXPORTS #define PROJECTAPI __declspec(dllexport)#else#define PROJECTAPI __declspec(dllimport)#endif#else#define PROJECTAPI#endif#endif

Then add "PROJECTAPI" to all classes.Define "USEPROJECTLIBRARY" only if you want export/import symbols from dll.Define "PROJECTLIBRARY_EXPORTS" for the dll.

Example of class export:

#include "ProjectExport.h"namespace hello {    class PROJECTAPI Hello {}   }

Example of function export:

#include "ProjectExport.h"PROJECTAPI void HelloWorld();

Caution: don't forget to include "ProjectExport.h" file.

1.2. Export as C functions.If you use C++ compiler for compilation code is written on C, you could add extern "C" in front of a function to eliminate name mangling

More info about C++ name mangling is provided by link:

Name Decoration

Example of usage:

extern "C" __declspec(dllexport) void HelloWorld();

More info about this is provided by link:

Exporting C++ Functions for Use in C-Language Executables

2. Create a module definition (.def) file and use the .def file when building the DLL

More info about this is provided by link:

Exporting from a DLL Using DEF Files

Further I describe three approach about how to create .def file.

2.1. Export C functions

In this case you could simple add function declarations in the .def file by hand.

Example of usage:

extern "C" void HelloWorld();

Example of .def file (__cdecl naming convention):

EXPORTS _HelloWorld

2.2. Export symbols from static library

I tried approach suggested by "user72260".

He said:

• Firstly, you could create static library.
• Then use "dumpbin /LINKERMEMBER" to export all symbols from static library.
• Parse the output.
• Put all results in a .def file.
• Create dll with the .def file.

I used this approach, but it's not very convinient to always create two builds (one as a static and the other as a dynamic library). However, I have to admit, this approach really works.

2.3. Export symbols from .obj files or with help of the CMake

2.3.1. With CMake usage

Important notice: You don't need any export macros to a classes or functions!

Important notice: You can't use /GL (Whole Program Optimization) when use this approach!

• Create CMake project based on the "CMakeLists.txt" file.
• Add the following line to the "CMakeLists.txt" file:set(CMAKE_WINDOWS_EXPORT_ALL_SYMBOLS ON)
• Then create Visual Studio project with help of "CMake (cmake-gui)".
• Compile the project.

Example of usage:

Root folder

CMakeLists.txt (Root folder)

cmake_minimum_required(VERSION 2.6)project(cmake_export_all)set(CMAKE_WINDOWS_EXPORT_ALL_SYMBOLS ON)set(dir ${CMAKE_CURRENT_SOURCE_DIR})set(CMAKE_RUNTIME_OUTPUT_DIRECTORY "${dir}/bin")set(SOURCE_EXE main.cpp)include_directories(foo)add_executable(main ${SOURCE_EXE})add_subdirectory(foo)target_link_libraries(main foo)

main.cpp (Root folder)

#include "foo.h"int main() {    HelloWorld();    return 0;}

Foo folder (Root folder / Foo folder)

CMakeLists.txt (Foo folder)

project(foo)set(SOURCE_LIB foo.cpp)add_library(foo SHARED ${SOURCE_LIB})

foo.h (Foo folder)

void HelloWorld();

foo.cpp (Foo folder)

#include <iostream>void HelloWorld() {    std::cout << "Hello World!" << std::endl;}

Link to the example project again:

cmake_windows_export_all_symbols

CMake uses the different from "2.2. Export symbols from static library" approach.

It does the following:

1) Create "objects.txt" file in the build directory with information of .obj files are used in a dll.

2) Compile the dll, that is create .obj files.

3) Based on "objects.txt" file information extract all symbols from .obj file.

Example of usage:

DUMPBIN /SYMBOLS example.obj > log.txt

More info about this is provided by link:

/SYMBOLS

4) Parse extracted from .obj file information.

In my opinion I would use calling convection, for example "__cdecl/__fastcall", "SECTx/UNDEF" symbol field (the third column), "External/Static" symbol field (the fifth column), "??", "?" information for parsing an .obj files.

I don't know how exactly CMake parse an .obj file.However, CMake is open source, so you could find out if it's interested for you.

Link to the CMake project:

CMake_github

5) Put all exported symbols in a .def file.

6) Link a dll with usage of a .def created file.

Steps 4)-5), that is parse .obj files and create a .def file before linking and using the .def file CMake does with help of "Pre-Link event".While "Pre-Link event" fires you could call any program you want.So in case of "CMake usage" "Pre-Link event" call the CMake with the following information about where to put the .def file and where the "objects.txt" file and with argument "-E __create_def".You could check this information by creating CMake Visusal Studio project with "set(CMAKE_WINDOWS_EXPORT_ALL_SYMBOLS ON)" and then check the ".vcxproj" project file for dll.

If you try to compile a project without "set(CMAKE_WINDOWS_EXPORT_ALL_SYMBOLS ON)" or with "set(CMAKE_WINDOWS_EXPORT_ALL_SYMBOLS OFF)" you will get linking errors, due to the fact that symbols are not exported from a dll.

More info about this is provided by link:

Understanding Custom Build Steps and Build Events

2.3.2. Without CMake usage

You simple could create a small program for parsing .obj file by youself without CMake usege. Hovewer, I have to admit that CMake is very usefull program especially for cross-platform development.

It can be done...

The way we do it here is to use the /DEF option of the linker to pass a "module definition file" containing a list of our exports. I see from your question that you know about these files. However, we do not do it by hand. The list of exports itself is created by the dumpbin /LINKERMEMBER command, and manipulating the output via a simple script to the format of a module definition file.

It is a lot of work to setup, but it allows us to compile code created without dllexport declarations for Unix on Windows.

I want to create a DLL and automatically export all symbols without adding __declspec(dllexport) everywhere and without hand-creating .def files. Is threre a way to do this?

This is a late answer, but it provides the details for Maks's answer in Section (2). It also avoids scripts and uses a C++ program called dump2def. The source code for dump2def is below.

Finally, the steps below assume you are working from a Visual Studio Developer Prompt, which is a Windows Terminal where vcvarsall.bat has been run. You need to ensure the build tools like cl.exe, lib.exe, link.exe and nmake.exe are on-path.

More info about this is provided by link:

Exporting from a DLL Using DEF Files
...

The instruction below use:

• static.lib - static library archive (*.a file on Linux)
• dynamic.dll - dynamic library (*.so file on Linux)
• import.lib - dynamic library (import library on Windows)

Also note that though you are exporting everything from the DLL, clients still must use declspec(dllimport) on all symbols (classes, functions and data) that they use. Also see on MSDN.

First, take your objects and create a static archive:

AR = lib.exeARFLAGS = /nologoCXX_SRCS = a.cpp b.cpp c.cpp ...LIB_OBJS = a.obj b.obj c.obj ...static.lib: $(LIB_OBJS)    $(AR) $(ARFLAGS) $(LIB_OBJS) /out:$@

Second, run dumpbin.exe /LINKERMEMEBER on the archive to create a *.dump file:

dynamic.dump:    dumpbin /LINKERMEMBER static.lib > dynamic.dump

Third, run dump2def.exe on the *.dump file to produce the *.def file. The source code for dump2def.exe is below.

dynamic.def: static.lib dynamic.dump    dump2def.exe dynamic.dump dynamic.def

Fourth, build the DLL:

LD = link.exeLDFLAGS = /OPT:REF /MACHINE:X64LDLIBS = kernel32.libdynamic.dll: $(LIB_OBJS) dynamic.def    $(LD) $(LDFLAGS) /DLL /DEF:dynamic.def /IGNORE:4102 $(LIB_OBJS) $(LDLIBS) /out:$@

/IGNORE:4102 is used to avoid this warning. It is expected in this case:

dynamic.def : warning LNK4102: export of deleting destructor 'public: virtual void * __ptr64 __cdecl std::exception::`scalar deleting destructor'(unsigned int) __ptr64'; image may not run correctly

When the dynamic.dll recipe is invoked, it creates a dynamic.lib import file and dynamic.exp file, too:

> cls && nmake /f test.nmake dynamic.dll...Creating library dynamic.lib and object dynamic.exp

And:

 C:\Users\Test\testdll>dir *.lib *.dll *.def *.exp Volume in drive C is Windows Volume Serial Number is CC36-23BE Directory of C:\Users\Test\testdll01/06/2019  08:33 PM        71,501,578 static.lib01/06/2019  08:33 PM        11,532,052 dynamic.lib Directory of C:\Users\Test\testdll01/06/2019  08:35 PM         5,143,552 dynamic.dll Directory of C:\Users\Test\testdll01/06/2019  08:33 PM         1,923,070 dynamic.def Directory of C:\Users\Test\testdll01/06/2019  08:35 PM         6,937,789 dynamic.exp               5 File(s)     97,038,041 bytes               0 Dir(s)  139,871,186,944 bytes free

Gluing it together here is what the Nmake makefile looks like. It is part of a real Nmake file:

all: test.exetest.exe: pch.pch static.lib $(TEST_OBJS)    $(LD) $(LDFLAGS) $(TEST_OBJS) static.lib $(LDLIBS) /out:$@static.lib: $(LIB_OBJS)    $(AR) $(ARFLAGS) $(LIB_OBJS) /out:$@dynamic.map:    $(LD) $(LDFLAGS) /DLL /MAP /MAPINFO:EXPORTS $(LIB_OBJS) $(LDLIBS) /out:dynamic.dlldynamic.dump:    dumpbin.exe /LINKERMEMBER static.lib /OUT:dynamic.dumpdynamic.def: static.lib dynamic.dump    dump2def.exe dynamic.dumpdynamic.dll: $(LIB_OBJS) dynamic.def    $(LD) $(LDFLAGS) /DLL /DEF:dynamic.def /IGNORE:4102 $(LIB_OBJS) $(LDLIBS) /out:$@clean:    $(RM) /F /Q pch.pch $(LIB_OBJS) pch.obj static.lib $(TEST_OBJS) test.exe *.pdb

And here is the source code for dump2def.exe:

#include <iostream>#include <fstream>#include <sstream>#include <string>#include <vector>#include <set>typedef std::set<std::string> SymbolMap;void PrintHelpAndExit(int code){    std::cout << "dump2def - create a module definitions file from a dumpbin file" << std::endl;    std::cout << "           Written and placed in public domain by Jeffrey Walton" << std::endl;    std::cout << std::endl;    std::cout << "Usage: " << std::endl;    std::cout << "  dump2def <infile>" << std::endl;    std::cout << "    - Create a def file from <infile> and write it to a file with" << std::endl;    std::cout << "      the same name as <infile> but using the .def extension" << std::endl;    std::cout << "  dump2def <infile> <outfile>" << std::endl;    std::cout << "    - Create a def file from <infile> and write it to <outfile>" << std::endl;    std::exit(code);}int main(int argc, char* argv[]){    // ******************** Handle Options ******************** //    // Convenience item    std::vector<std::string> opts;    for (size_t i=0; i<argc; ++i)        opts.push_back(argv[i]);    // Look for help    std::string opt = opts.size() < 3 ? "" : opts[1].substr(0,2);    if (opt == "/h" || opt == "-h" || opt == "/?" || opt == "-?")        PrintHelpAndExit(0);    // Add <outfile> as needed    if (opts.size() == 2)    {        std::string outfile = opts[1];        std::string::size_type pos = outfile.length() < 5 ? std::string::npos : outfile.length() - 5;        if (pos == std::string::npos || outfile.substr(pos) != ".dump")            PrintHelpAndExit(1);        outfile.replace(pos, 5, ".def");        opts.push_back(outfile);    }    // Check or exit    if (opts.size() != 3)        PrintHelpAndExit(1);    // ******************** Read MAP file ******************** //    SymbolMap symbols;    try    {        std::ifstream infile(opts[1].c_str());        std::string::size_type pos;        std::string line;        // Find start of the symbol table        while (std::getline(infile, line))        {            pos = line.find("public symbols");            if (pos == std::string::npos) { continue; }                    // Eat the whitespace after the table heading            infile >> std::ws;            break;        }        while (std::getline(infile, line))        {            // End of table            if (line.empty()) { break; }            std::istringstream iss(line);            std::string address, symbol;            iss >> address >> symbol;            symbols.insert(symbol);        }    }    catch (const std::exception& ex)    {        std::cerr << "Unexpected exception:" << std::endl;        std::cerr << ex.what() << std::endl;        std::cerr << std::endl;        PrintHelpAndExit(1);    }    // ******************** Write DEF file ******************** //    try    {        std::ofstream outfile(opts[2].c_str());        // Library name, cryptopp.dll        std::string name = opts[2];        std::string::size_type pos = name.find_last_of(".");        if (pos != std::string::npos)            name.erase(pos);        outfile << "LIBRARY " << name << std::endl;        outfile << "DESCRIPTION \"Crypto++ Library\"" << std::endl;                outfile << "EXPORTS" << std::endl;        outfile << std::endl;        outfile << "\t;; " << symbols.size() << " symbols" << std::endl;        // Symbols from our object files        SymbolMap::const_iterator it = symbols.begin();        for ( ; it != symbols.end(); ++it)            outfile << "\t" << *it << std::endl;    }    catch (const std::exception& ex)    {        std::cerr << "Unexpected exception:" << std::endl;        std::cerr << ex.what() << std::endl;        std::cerr << std::endl;        PrintHelpAndExit(1);    }       return 0;}