Cmake windows export all symbols

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.

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.

Время на прочтение
2 мин

Количество просмотров 36K

Введение

CMake (от англ. cross platform make) — это кроссплатформенная система автоматизации сборки программного обеспечения из исходного кода.

CMake не занимается непосредственно сборкой, a лишь генерирует файлы управления сборкой из файлов CMakeLists.txt.

Динамические библиотеки. Теория

Создание динамических библиотек со статической линковкой в ОС Windows отличается от ОС GNU/Linux.

На ОС Windows для этого требуется связка .dll (dynamic link library) + .lib (library) файлов.
На ОС GNU/Linux для этого нужен всего лишь один .so (shared object) файл.

Динамические библиотеки. Практика

На практике хочется писать удобный, одинаковый код на обеих ОС.

В каждом проекте (или на несколько проектов одна) присутствовала условная компиляция:

#ifndef __linux__
    #if defined( <target_name>_EXPORTS )
        #define DLL_<target_name>_EXPORT __declspec(dllexport)
    #else // !BUILDING_DLL
        #define DLL_<target_name>_EXPORT __declspec(dllimport)
    #endif // BUILDING_DLL
#else
    #define DLL_<target_name>_EXPORT
#endif // __linux__

Соответственно, для каждого экспортируемого класса из библиотеки необходимо прописать данный макрос:

class DLL_<target_name>_EXPORT <class_name>

В данном случае, на ОС Windows экспортируются все классы/методы, которые помечены данным макросом, а на ОС GNU/Linux, по умолчанию, всё экспортируется, т.к. нет макроса для скрытия классов/методов.

С выходом CMake версии 3.4.0, стало возможным создание библиотек с классами, которые экспортируются по умолчанию. Для этого в каждой цели (target), которые объявлены как SHARED (динамическая библиотека), необходимо включить свойство:

set ( CMAKE_WINDOWS_EXPORT_ALL_SYMBOLS ON)

Пример небольшой библиотеки:

# Проверка версии CMake
cmake_minimum_required( VERSION 3.4.0 )
# Если версия установленой программы ниже, то ошибка выполнения

# Название проекта и проверка доступности компиляторя с++
project( shared_lib CXX )			

# Установка переменной со списком исходников
set( SOURCE_LIB example.cpp )		

# Включение экспорта всех символов для создания динамической библиотеки
set ( CMAKE_WINDOWS_EXPORT_ALL_SYMBOLS ON )

# Создание динамической библиотеки с именем example
add_library( example SHARED ${SOURCE_LIB} )	

И убрать определение и использование макросов из кода:

DLL_<target_name>_EXPORT

Данное свойство автоматически создает module definition (.def) со всеми глобальными символами из .obj файла для динамической библиотеки на ОС Windows.

Далее данный файл (.def) передается компоновщику для создания .lib файла. На выходе на ОС Windows получается связка .lib + .dll

Итоги

Код стал более читабельным, нет лишних строчек. И вероятность появления ошибки во время неправильного написания блока условной компиляции и определения макроса среди разработчиков сведена к нулю. В CMakeLists файле всего одна дополнительная строчка.