Can't Cross Compiling jsoncpp 00.11.z for aarch64

[Derrekito]

Can't seem to get cross-compiling working I'm trying to cross compile from x86_64 host for an ARM64 target.

To Reproduce Steps to reproduce the behavior: 1.cmake -DCMAKE_INSTALL_PREFIX=/usr/aarch64-linux-gnu \ -DCMAKE_SYSTEM_NAME=Linux \ -DCMAKE_SYSTEM_PROCESSOR=aarch64 \ -DCMAKE_C_COMPILER=aarch64-linux-gnu-gcc \ -DCMAKE_CXX_COMPILER=aarch64-linux-gnu-g++ \ ..\ && make

2. file lib/libjsoncpp.so.00.11.0 lib/libjsoncpp.so.00.11.0: ELF 64-bit LSB shared object, x86-64, version 1 (SYSV), dynamically linked, BuildID[sha1]=9b7e6633cefe354d240f3524a8dda7a25abfd683, not stripped

Expected behavior produce an aarch64 object.

Desktop (please complete the following information):

• OS: ubuntu 20.04

[BillyDonahue]

Does this cmake invocation usually work? Can you cross-compile other projects successfully with those options?

[Derrekito]

I appreciate your response. However, I usually avoid cmake, so I cannot adequately answer your question. But I've tried passing some of these cross-compilation flags directly and also by creating and passing a toolchain file.

https://cmake.org/cmake/help/book/mastering-cmake/chapter/Cross%20Compiling%20With%20CMake.html

Here's my aarch-toochain.cmake file

# aarch64-toolchain.cmake

# Set the target system name
set(CMAKE_SYSTEM_NAME Linux)
set(CMAKE_SYSTEM_PROCESSOR aarch64)

# Set the cross compilers
set(bin_path /usr/bin)
set(CMAKE_C_COMPILER ${bin_path}/aarch64-linux-gnu-gcc)
set(CMAKE_CXX_COMPILER ${bin_path}/aarch64-linux-gnu-g++)

# Set the target architecture
set(CMAKE_SYSTEM_PROCESSOR aarch64)

here's my cmake .. -DCMAKE_TOOLCHAIN_FILE=../aarch-toolchain.cmake output

-- The CXX compiler identification is GNU 11.4.0
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: /usr/bin/aarch64-linux-gnu-g++ - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- JsonCpp Version: 00.11.0
-- Compiled with C++11(or newer) standard!
-- Looking for C++ include clocale
-- Looking for C++ include clocale - found
-- Looking for localeconv
-- Looking for localeconv - found
-- Looking for C++ include sys/types.h
-- Looking for C++ include sys/types.h - found
-- Looking for C++ include stdint.h
-- Looking for C++ include stdint.h - found
-- Looking for C++ include stddef.h
-- Looking for C++ include stddef.h - found
-- Check size of lconv
-- Check size of lconv - done
-- Performing Test HAVE_DECIMAL_POINT
-- Performing Test HAVE_DECIMAL_POINT - Success
-- Found Python3: /usr/bin/python3.10 (found version "3.10.12") found components: Interpreter
-- Configuring done
-- Generating done
-- Build files have been written to: /home/derrekito/Downloads/jsoncpp/build

It seems to skip looking at CXX processor, which makes me think this has something to do with the project defaulting to my host compiler.

[BillyDonahue]

I don't know cmake very well.

This line is very suspicious:

    -- Check for working CXX compiler: /usr/bin/aarch64-linux-gnu-g++ - skipped

There's sometimes a config log you can look at to see deeper diagnostics? Maybe someone else with more cmake experience can chime in?

[Derrekito]

My CMakeCache.txt seems to suggest that CMAKE is recognizing the cross-compile args, but isn't actually producing a cross-compiled object.

cat CMakeCache.txt | grep aarch64
CMAKE_ADDR2LINE:FILEPATH=/usr/bin/aarch64-linux-gnu-addr2line
CMAKE_AR:FILEPATH=/usr/bin/aarch64-linux-gnu-ar
CMAKE_CXX_COMPILER_AR:FILEPATH=/usr/bin/aarch64-linux-gnu-gcc-ar-11
CMAKE_CXX_COMPILER_RANLIB:FILEPATH=/usr/bin/aarch64-linux-gnu-gcc-ranlib-11
CMAKE_LINKER:FILEPATH=/usr/bin/aarch64-linux-gnu-ld
CMAKE_NM:FILEPATH=/usr/bin/aarch64-linux-gnu-nm
CMAKE_OBJCOPY:FILEPATH=/usr/bin/aarch64-linux-gnu-objcopy
CMAKE_OBJDUMP:FILEPATH=/usr/bin/aarch64-linux-gnu-objdump
CMAKE_RANLIB:FILEPATH=/usr/bin/aarch64-linux-gnu-ranlib
CMAKE_READELF:FILEPATH=/usr/bin/aarch64-linux-gnu-readelf
CMAKE_STRIP:FILEPATH=/usr/bin/aarch64-linux-gnu-strip
CMAKE_TOOLCHAIN_FILE:FILEPATH=/home/derrekito/Downloads/jsoncpp/aarch64-toolchain.cmake

[Derrekito]

CMakeLists.txt is overriding the compiler settings. Commenting out the set(CMAKE_CXX_COMPILER "/usr/bin/g++") line fixed my issue.

file lib/libjsoncpp.so.00.11.0
lib/libjsoncpp.so.00.11.0: ELF 64-bit LSB shared object, ARM aarch64, version 1 (SYSV), dynamically linked, BuildID[sha1]=c0f7bfaca719ab7e6a28dd6f21a382192cdebff2, not stripped

I'll edit the CMakeLists.txt to check for the flag before clobbering such settings.

if(NOT CMAKE_CXX_COMPILER)
    set(CMAKE_CXX_COMPILER "/usr/bin/g++")
endif()

The only issue now is that tests fail when the compiled object isn't meant for the host system. Should I press with a pull request anyway??