I have two shared libraries: liba and libb, where libb depends on liba and an executable which uses libb. I faced a problem building the project using CMake for aarch64 architecture, while everything works fine with host toolchain. The project looks as following:
├── CMakeLists.txt
├── liba
│ └── main.cpp
├── libb
│ └── main.cpp
└── main
└── main.cpp
CMakeLists.txt content is the following:
cmake_minimum_required(VERSION 3.15)
project(my_proj CXX)
add_library(a SHARED liba/main.cpp)
set_property(TARGET a PROPERTY LIBRARY_OUTPUT_DIRECTORY "${CMAKE_CURRENT_BINARY_DIR}/a")
add_library(b SHARED libb/main.cpp)
set_property(TARGET b PROPERTY LIBRARY_OUTPUT_DIRECTORY "${CMAKE_CURRENT_BINARY_DIR}/b")
target_link_libraries(b PRIVATE a)
add_executable(main main/main.cpp)
target_link_libraries(main b)
Everything works completely fine with my host g++/ld compiler/linker. However, when I try to build the project using ARM compiler, I get linker error:
$ cmake .. -DCMAKE_CXX_COMPILER=aarch64-linux-gnu-g++
-- The CXX compiler identification is GNU 9.2.0
-- Check for working CXX compiler: /usr/bin/aarch64-linux-gnu-g++
-- Check for working CXX compiler: /usr/bin/aarch64-linux-gnu-g++ -- works
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Configuring done
-- Generating done
-- Build files have been written to: /home/icblnk/tmp/rm/test/build
$ make
Scanning dependencies of target a
[ 16%] Building CXX object CMakeFiles/a.dir/liba/main.cpp.o
[ 33%] Linking CXX shared library a/liba.so
[ 33%] Built target a
Scanning dependencies of target b
[ 50%] Building CXX object CMakeFiles/b.dir/libb/main.cpp.o
[ 66%] Linking CXX shared library b/libb.so
[ 66%] Built target b
Scanning dependencies of target main
[ 83%] Building CXX object CMakeFiles/main.dir/main/main.cpp.o
[100%] Linking CXX executable main
/usr/lib/gcc/aarch64-linux-gnu/9.2.0/../../../../aarch64-linux-gnu/bin/ld: warning: liba.so, needed by b/libb.so, not found (try using -rpath or -rpath-link)
/usr/lib/gcc/aarch64-linux-gnu/9.2.0/../../../../aarch64-linux-gnu/bin/ld: b/libb.so: undefined reference to `function_liba_1()'
collect2: error: ld returned 1 exit status
make[2]: *** [CMakeFiles/main.dir/build.make:85: main] Error 1
make[1]: *** [CMakeFiles/Makefile2:78: CMakeFiles/main.dir/all] Error 2
make: *** [Makefile:84: all] Error 2
The problem is that CMake uses rpath ELF entries to find PRIVATE libraries, which for some reason doesn't work in case of ARM's linker. I tried to look into possible linker options, but failed to find anything useful.
compiler/linker versions I used in the example:
$ ld --version
GNU ld (GNU Binutils) 2.32
$ aarch64-linux-gnu-ld --version
GNU ld (GNU Binutils) 2.32
$ g++ --version
g++ (GCC) 9.2.0
$ aarch64-linux-gnu-g++ --version
aarch64-linux-gnu-g++ (GCC) 9.2.0