Embedded Linux-ARMV7 Cross Compilation with Musl-LibC

CMakeLists.txt

cmake_minimum_required(VERSION 3.9)
project(embedded-linux-armv7)

set(CMAKE_CXX_STANDARD 17)     
set(CMAKE_VERBOSE_MAKEFILE ON)

#====== Global compiler and linker settings ======#

# (-static)           => Fully statically link Musl-LibC
# (-Wl,--gc-sections) => Remove unused code
#                        (requires: -fdata-sections and -ffunction-sections)
set(CMAKE_EXE_LINKER_FLAGS "-static -Wl,--gc-sections")

# Separate data and code sections in order to reduce binary size. 
add_definitions( -fdata-sections -ffunction-sections )

# Copy target executable, for instance my-exe to my-exe.debug 
# and strip debugging symbols from my-exe.
# 
# Reference: https://cmake.org/pipermail/cmake/2011-October/046743.html
macro(STRIP_DEBUG_SYMBOLS target)
  ADD_CUSTOM_COMMAND(TARGET ${target} POST_BUILD
    COMMAND ${CMAKE_COMMAND} -E copy $<TARGET_FILE:${target}> ${CMAKE_BINARY_DIR}/${target}.debug
    COMMAND ${CMAKE_STRIP} -g $<TARGET_FILE:${target}>
  )
endmacro()

#========== Targets Configurations ============#

        add_executable( app portable-app.cpp )
 target_link_libraries( app stdc++fs)
   STRIP_DEBUG_SYMBOLS( app )

Dockerfile.docker

FROM muslcc/i686:armv7l-linux-musleabihf
RUN  apk add make cmake 

# ENTRYPOINT ["cmake"]

Makefile

DOCKER_COMMAND=docker run -e UID=$(shell id -u) -e GID=$(shell id -g) --volume=$(shell pwd):/cwd  --workdir=/cwd musl-armv7

# Builds docker image: musl-armv7
docker:
	docker build -f Dockerfile.docker -t musl-armv7 .

# Build testing application 
build:
	${DOCKER_COMMAND} cmake -H. -B_build-armv7 -DCMAKE_BUILD_TYPE=Debug
	${DOCKER_COMMAND} cmake --build _build-armv7 --target 

clean:
	rm -rf -v _build-armv7

portable-app.cpp

#include <iostream>
#include <string>
#include <algorithm>
#include <iomanip>
#include <filesystem>
#include <fstream> 
#include <cassert> 

namespace fs = std::filesystem;

int main(int argc, char** argv)
{

  assert( argc >= 2 && "Supposed to have at least one arguments");
  std::cout << std::boolalpha;
  std::string command = argv[1];

  if(command == "version")
  { 
      auto ifs = std::ifstream("/proc/version");
      assert( ifs.good() && "File supposed to exist" );  
      std::cout << ifs.rdbuf();
      return EXIT_SUCCESS;
  }
  
  std::cout << "\n ===== Listing directory /etc =====" << std::endl;

  if(command == "list")
  {
      // Show first 10 files of directory /etc 
    auto iter = fs::directory_iterator(argv[2]);

    std::for_each(fs::begin(iter), fs::end(iter)
		 ,[](auto p){
		   auto path = p.path();
		   std::cout << std::left
			     << std::setw(0) << path.filename().string()
			     << " " << std::setw(35)
			     << std::right << std::setw(40) << path
			     << std::endl;				
		 });    
    return EXIT_FAILURE;    
  }
  
  return EXIT_SUCCESS;
}