Building shared library which is executable and linkable using Cmake

Question

How to create an executable shared-library using cmake?

Something like:

libtest.so :: linkable shared library

libtest.so :: executable too

Note: gcc/g++ options are known to achieve the same (https://unix.stackexchange.com/a/223411/152034). But the solution needs cmake way

Solution

NOTE: First information regarding this is, there is seemingly an open issue related to cmake. Therefore this can be considered as an indirect solution to achieve the same.

Now follow the illustration using cmake.

test.cpp

#include <stdio.h>                  
void sayHello (char *tag) {         
    printf("%s: Hello!\n", tag);    
}                                
int main (int argc, char *argv[]) { 
    sayHello(argv[0]);              
    return 0;                       
}

ttest/test_test.cpp

#include <stdio.h>                  
extern void sayHello (char*);
int main (int argc, char *argv[]) { 
    printf("\nNow Inside test-test !\n");    
    sayHello(argv[0]);              
    return 0;                       
}

CMakeLists.txt

cmake_minimum_required(VERSION 3.5)
project(pie_test)
#shared-lib as executable
add_library(${PROJECT_NAME} SHARED
            test.cpp
)
target_compile_options(${PROJECT_NAME} PUBLIC "-pie")
target_link_libraries(${PROJECT_NAME} "-pie -Wl,-E")
set_property(TARGET ${PROJECT_NAME} PROPERTY POSITION_INDEPENDENT_CODE 1)
#executable linking to the executable-shared-library
add_executable(test_test
               ttest/test_test.cpp
)
target_link_libraries(test_test pie_test)
set_property(TARGET test_test PROPERTY POSITION_INDEPENDENT_CODE 1)

build.sh

#!/bin/bash
rm -rf build
mkdir build
cd build
cmake .. #--debug-output
make VERBOSE=1
echo "Done!"
echo ""

Reference for gcc-options here.

Comments

[goldilocks]

I don't think that bug report pertains exactly to this; PIC and PIE are not the same. Shared library code by default requires -fPIC, but it does not require -pie. Using PROPERTY POSITION_INDEPENDENT_CODE should only do the former, or, as the last poster there says, it should do it for executables -- and a shared library in a cmake context is not an executable. But you can still add -pie if you like. Did you try using target_compile_options?

[parasrish]

1) I understand, pic and pie not the same. However, by the cmake discussions, seems they "do not have support for pie" directly as such. Now addressing the case, by introducing new flag (something like - position_independent_executable) or in some other way, is not being concluded. The reference, was to aware, about an open discussion in this front at cmake forum. 2) And after all, that has been tried, the posted one seems to be working (target_compile_options used with parameters as above).

[FeRD]

Just last week, it appears, the MR to resolve that discussion was merged, so in bleeding-edge / future cmake the target_compile_options / target_link_libraries lines should no longer be necessary, as the relevant flags will be automatically added by the POSITION_INDEPENDENT_CODE property.