[CMake] cross-compiling for arm

[Rolf Eike Beer]

Gunter, Walter E wrote:
> I setup the Main CMakeLists.txt to cross_compile using an arm toolchain:
> 
> cmake_minimum_required(VERSION 3.2)
> 
> project(enterprise CXX)
> 
> set(CMAKE_SYSTEM_NAME Linux)
> set(CMAKE_CXX_COMPILER
> /opt/toolchains/arm-2008q3/bin/arm-none-linux-gnueabi-g++)
> set(CMAKE_SYSTEM_PROCESSOR arm)
> 
> set(CMAKE_AR /opt/toolchains/arm-2008q3/bin/arm-none-linux-gnueabi-ar)
> set(CMAKE_FIND_ROOT_PATH /mnt/root)
> 
> set(CMAKE_FIND_ROOT_PATH_MODE_PROGRAM NEVER)
> set(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY)
> set(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)
> set(CMAKE_FIND_ROOT_PATH_MODE_PACKAGE ONLY)
> 
> set(COMPILE_FLAGS "-lrt -Wall -lpthread")
> 
> find_package(Threads)
> 
> add_subdirectory(src)
> 
> if(CMAKE_CROSSCOMPILING)
>      message("I should be cross compiling: ")
> endif()
> 
> #find_package(GTest REQUIRED)
> 
> --------------------------------------------------------
> 
> I made some changes to my cmakelists.txt in my src file :
> 
> set(SOURCES  ${CMAKE_CURRENT_SOURCE_DIR}
> *list of files*.cpp
> Mainfile.cpp
> Mycan.cpp   #this one references the linux/can.h
> )
> 
> include_directories("../includes")
> set_source_files_properties(${SOURCES} PROPERTIES LANGUAGE CXX)

This is not needed, CMake will automatically detect this.

> add_executable(enterprise ${SOURCES})
> target_link_libraries(enterprise  ${CMAKE_THREAD_LIBS_INIT} pthread)

pthread is not needed here. If CMAKE_THREAD_LIBS_INIT is empty you probably 
have a problem already. Also you should do

set(CMAKE_THREAD_PREFER_PTHREAD TRUE)

before find_package(Threads), and ideally

target_link_libraries(enterprise Threads::Threads)

afterwards, as this will also add the -pthread flag to compilation.

I still doubt that you properly use a toolchain file (i.e. "cmake -D 
CMAKE_TOOLCHAIN_FILE=my_arm_stuff.cmake …" in a clean build dir).

Eike
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