CMake cannot detect symbol conflicts in different static libraries

Question

I created a simple cmake project to reproduct it.

├── CMakeLists.txt
├── lib1
│   ├── CMakeLists.txt
│   ├── lib1.cpp
│   └── lib1.h
├── lib2
│   ├── CMakeLists.txt
│   ├── lib2.cpp
│   └── lib2.h
└── main.cpp

lib1/CMakeLists.txt:

add_library(lib1 "")
target_include_directories(lib1
  PUBLIC
      ${CMAKE_CURRENT_LIST_DIR}
)
target_sources(lib1
    PRIVATE
        lib1.cpp
        lib1.h
)

In lib1.cpp, there is a function "void say()":

#include <stdio.h>

void say()
{
    printf("hello from lib1\n");
}

lib2/CMakeLists.txt:

add_library(lib2 "")
target_include_directories(lib2
  PUBLIC
      ${CMAKE_CURRENT_LIST_DIR}
)
target_sources(lib2
    PRIVATE
        lib2.cpp
        lib2.h
)

And in lib2/lib2.cpp, there is a function of the same signature:

#include <stdio.h>
void say()
{
    printf("hello from lib2\n");
}

CMakeLists.txt:

cmake_minimum_required(VERSION 3.16)
project(shell LANGUAGES CXX)
add_subdirectory(lib1)
add_subdirectory(lib2)
add_executable(test2
  main.cpp
)
target_link_libraries(test2
  PRIVATE
    lib1
    lib2
)

Here is the main.cpp:

void say();
int main()
{
    say();
    return 0;
}

The output:

hello from lib1

There is no compile or link error, not even a warning. The linker just picked one and symply ignored the other one. I'm using cmake 3.16, and tested it with msvc 2017/2019 and g++ 7.5.

How to make the linker prompts errors when there are symbol conflicts in static libraries?

Thanks!

Can you show the CMakeLists.txt? Linking only happens when you actually link everything into an executable. But you should specify that in your CMakeLists.txt for the application, something like: add_executable( main ); target_link_libraries( main lib1 lib2 ) — André
It doesn't have to do with CMake. See Why C++ linker is silent about ODR violation? — Joel Filho
It may be not to do with CMake, but there should be a way to make it work in CMake No, this has nothing to do with cmake. Cmake doesn't compile your code. — KamilCuk

KamilCuk KamilCuk · Accepted Answer · 2020-04-19T09:10:11

How to make the linker prompts errors when there are symbol conflicts in static libraries?

With gcc use the --whole-archive option to include every object file in the archive rather then search the archives for the required symbol.

As there is no cmake support that I know of, I find it's typically done when linking the executable:

target_link_libraries(test2 PRIVATE
    -Wl,--whole-archive
    lib1
    lib2
    -Wl,--no-whole-archive
)

"Symbol conflicts" is rather vague term. This will only detect multiple symbol definitions. Types of symbols are not stored anywhere after compilation.

CMake cannot detect symbol conflicts in different static libraries

1 Answers