Linking statically OpenSSL crypto library in CMake

Question

I want to statically link the libraries listed below:

set_target_properties(exec PROPERTIES LINK_SEARCH_START_STATIC 1)
set_target_properties(exec PROPERTIES LINK_SEARCH_END_STATIC 1)
set(CMAKE_FIND_LIBRARY_SUFFIXES .a ${CMAKE_FIND_LIBRARY_SUFFIXES})

find_library(SODIUM_LIB libsodium.a REQUIRED)
find_library(SSL_LIB libssl.a REQUIRED)
find_library(CRYPTO_LIB libcrypto.a REQUIRED)
find_library(DL_LIB libdl.a REQUIRED)

message(${SODIUM_LIB})
message(${SSL_LIB})
message(${CRYPTO_LIB})

set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -static-libgcc -static-libstdc++")

target_link_libraries(
    exec
    ${SODIUM_LIB}
    ${SSL_LIB}
    ${CRYPTO_LIB}
    ${DL_LIB}

I do not want to add -static to CMAKE_EXE_LINKER_FLAGS, because in that case everything is linked static. CMake finds the static libraries:

/usr/local/lib/libsodium.a
/usr/lib/x86_64-linux-gnu/libssl.a
/usr/lib/x86_64-linux-gnu/libcrypto.a

and it seems that everything is linked statically except libcrypto:

readelf -d exec
 0x0000000000000001 (NEEDED)             Shared library: [libcrypto.so.1.0.0]
 0x0000000000000001 (NEEDED)             Shared library: [libc.so.6]
 0x0000000000000001 (NEEDED)             Shared library: [ld-linux-x86-64.so.2]

How can I link libcrypto statically to my executable?

Answer 1

The CMake documentation starting with version 3.4 on the FindOpenSSL page says:

Set OPENSSL_USE_STATIC_LIBS to TRUE to look for static libraries.

(Assuming if they are found they will be used)

Example:

cmake_minimum_required(VERSION 3.4)
project(Foo)

set(SOURCE_FILES main.cpp)

set(OPENSSL_USE_STATIC_LIBS TRUE)
find_package(OpenSSL REQUIRED)

add_executable(${PROJECT_NAME} ${SOURCE_FILES})
target_link_libraries(${PROJECT_NAME} OpenSSL::Crypto)