Link error undefined reference to `pthread_atfork`

[jimlloyd]

I am trying to use your project to build openssl for arm64. It largely works. Our (private) repo has dozen or so targets that depend on openssl, and many of then compile and link fine. But a few are failing with an error like this:

opt/openssl-cmake/usr/local/lib/libcrypto.a(threads_pthread.o): In function `fork_once_func':
threads_pthread.c:(.text+0x18): undefined reference to `pthread_atfork'

It seems that CMake is unable to enforce a dependency from crypto to pthread. For some apps, the link order is coincidentally correct, but for other apps the link order is wrong, and this error occurs.

I have tried modifying the CMakeLists.txt. The simplest change that I thought might work was just to declare the dependency on pthread like this:

target_link_libraries(crypto INTERFACE crypto_lib pthread)

That doesn't seem to work. It might work if we could make the dependency be on crypto instead of crypto_lib, but that fails because crypto is not built in this project.

I'm reasonably well-versed with CMake but not a true expert. Do you see a way forward here?

I think I have a somewhat hacky workaround, which is to build openssl in a separate repo, and then just check in the headers had libraries into our main repo and wrap then as a CMake STATIC IMPORTED target. But if you know how to solve this it would be nice to eliminate that hack.

[roussosalex]

Could you provide us with a minimal example for reproduction? Your changes look correct to me, maybe there is a ordering issue of linked libraries. Could you run a verbose make and check the order of linked libraries in the final linker command?