Enable arm cross building (wateret#56)

This will enable cross building for ARM
- Tested with Raspberry Pi 3 with rpi SDL backend

CMakeLists.txt

@@ -22,11 +22,22 @@ elseif (${CMAKE_CXX_COMPILER_ID} STREQUAL "MSVC")
     endif()
 endif()
 
+set(BUILD_NATIVE True)
+if(DEFINED ROOTFS_ARM)
+    set(BUILD_NATIVE False)
+endif()
+
 # Look up required packages and add the include directory to our include path
-find_package(Boost 1.55.0 COMPONENTS filesystem system REQUIRED)
-find_package(SDL2 REQUIRED)
-find_package(SDL2_ttf REQUIRED)
-find_package(Lua REQUIRED)
+if(BUILD_NATIVE)
+    find_package(Boost 1.55.0 COMPONENTS filesystem system REQUIRED)
+    find_package(SDL2 REQUIRED)
+    find_package(SDL2_ttf REQUIRED)
+    find_package(Lua REQUIRED)
+else()
+    if (DEFINED ROOTFS_ARM)
+        include("cmake/armv7l_settings.cmake")
+    endif()
+endif()
 include_directories(${Boost_INCLUDE_DIR})
 include_directories(${SDL2_INCLUDE_DIR})
 include_directories(${SDL2_TTF_INCLUDE_DIR})

README.md

@@ -67,6 +67,26 @@ $ docker build -t {image_tag_name} docker
 $ docker run --rm -v `pwd`:{mount_path_on_container} -w={mount_path_on_container} {image_tag_name} ./build.py
 ```
 
+##### Cross build for ARM(Raspberry Pi 2/3)
+
+You need to install required packages
+```
+sudo apt-get install qemu qemu-user-static binfmt-support debootstrap
+sudo apt-get install binutils-arm-linux-gnueabihf
+sudo apt-get install gcc-arm-linux-gnueabihf g++-arm-linux-gnueabihf
+```
+
+You then need to prepare a root filesystem. Only ARMv7l is supported for now.
+```
+$ sudo ./cross/build-rootfs.sh
+```
+Root file system will be prepared in `./cross/rootfs/armv7l`
+
+After it's prepared, you can build with `--cross` option.
+```
+$ ./build.py --cross armv7l
+```
+
 #### Windows
 
 TBD

build.py

@@ -69,6 +69,7 @@ def parse_args():
     parser.add_argument("--buildpath", default="build", help="specify build path")
     parser.add_argument("--clean",     default=False,   help="clean before build", dest="clean", action="store_true")
     parser.add_argument("--single",    default=False,   help="disalbe parallel build", dest="single", action="store_true")
+    parser.add_argument("--cross",     default="",      help="cross build target", choices=["", "armv7l"])
 
     return parser.parse_args()
 
@@ -79,17 +80,33 @@ def main():
     system, node, release, version, machine, processor = platform.uname()
     cpu_count = multiprocessing.cpu_count()
 
+    if options.cross == "armv7l":
+        machine = "armv7l"
+
     # Set the install folder
     install_folder = "mengde"
 
+    home_folder = os.getcwd()
+
     print_header("Start CMake configuration")
     build_dir = "build/%s.%s.%s" % (system, machine, options.buildtype)
     check_run_cmd("mkdir", ["-p", build_dir])
     os.chdir(build_dir)
-    check_run_cmd("cmake", ["-DCMAKE_BUILD_TYPE=" + options.buildtype,
-                            ("../" * (build_dir.count("/") + 1)),
-                            "-DCMAKE_INSTALL_PREFIX=./",
-                            "-DINSTALL_FOLDER=" + install_folder])
+
+    if options.cross == "armv7l":
+        if os.environ.get("ROOTFS_ARM") is None:
+            os.environ["ROOTFS_ARM"] = os.path.join(home_folder, "cross/rootfs/armv7l")
+        toolchain = os.path.join(home_folder, "cmake/toolchain-armv7l.cmake")
+        check_run_cmd("cmake", ["-DCMAKE_BUILD_TYPE=" + options.buildtype,
+                                ("../" * (build_dir.count("/") + 1)),
+                                "-DCMAKE_INSTALL_PREFIX=./",
+                                "-DINSTALL_FOLDER=" + install_folder,
+                                "-DCMAKE_TOOLCHAIN_FILE=" + toolchain])
+    else:
+        check_run_cmd("cmake", ["-DCMAKE_BUILD_TYPE=" + options.buildtype,
+                                ("../" * (build_dir.count("/") + 1)),
+                                "-DCMAKE_INSTALL_PREFIX=./",
+                                "-DINSTALL_FOLDER=" + install_folder])
 
     # From here, support `Makefile` project only
     make_args = []

cmake/armv7l_settings.cmake

@@ -0,0 +1,36 @@
+# Notice: this file is used in cross building for ARMv7l
+# find_package() will be looking for host machine 
+# and it will not be correct for cross building for ARM target.
+# As RootFS will be prepared with required packages,
+# we assume they are installed as described in below folders.
+
+if(NOT DEFINED ROOTFS_ARM)
+    message(FATAL_ERROR "ROOTFS_ARM is required for cross building")
+endif()
+if(NOT ${CMAKE_SYSTEM_NAME} STREQUAL "Linux")
+    message(FATAL_ERROR "ARM cross build is currently supported only in Linux")
+endif()
+if(NOT EXISTS "${ROOTFS_ARM}/lib/arm-linux-gnueabihf")
+    message(FATAL_ERROR "ROOTFS_ARM path doesn't seem to be a correct ARM rootfs")
+endif()
+
+set(Boost_VERSION 105500)
+set(Boost_FOUND True)
+set(BOOST_INCLUDEDIR ${ROOTFS_ARM}/usr/include/boost)
+set(BOOST_LIBRARYDIR ${ROOTFS_ARM}/usr/lib/arm-linux-gnueabihf)
+set(Boost_INCLUDE_DIRS ${ROOTFS_ARM}/usr/include/boost)
+set(SDL2_INCLUDE_DIR ${ROOTFS_ARM}/usr/include/SDL2)
+set(SDL2_TTF_INCLUDE_DIR ${ROOTFS_ARM}/usr/include/SDL2)
+set(LUA_INCLUDE_DIR ${ROOTFS_ARM}/usr/include/lua5.2)
+
+set(SDL2_LIBRARY SDL2main SDL2 pthread)
+set(SDL2_TTF_LIBRARIES SDL2_ttf)
+set(Boost_LIBRARIES boost_filesystem boost_system)
+set(LUA_LIBRARIES lua5.2 m)
+
+# include path for system
+include_directories(${ROOTFS_ARM}/usr/include/arm-linux-gnueabihf)
+
+# library path for system
+link_directories(${ROOTFS_ARM}/usr/lib/arm-linux-gnueabihf
+                 ${BOOST_LIBRARYDIR})

cmake/toolchain-armv7l.cmake

@@ -0,0 +1,24 @@
+include(CMakeForceCompiler)
+
+set(CMAKE_SYSTEM_NAME Linux)
+set(CMAKE_SYSTEM_PROCESSOR armv7l)
+
+SET(CMAKE_C_COMPILER   arm-linux-gnueabihf-gcc)
+SET(CMAKE_CXX_COMPILER arm-linux-gnueabihf-g++)
+
+# where is the target environment
+set(ROOTFS_ARM $ENV{ROOTFS_ARM})
+set(CMAKE_SHARED_LINKER_FLAGS
+    "${CMAKE_SHARED_LINKER_FLAGS} --sysroot=${ROOTFS_ARM}"
+    CACHE INTERNAL "" FORCE)
+set(CMAKE_EXE_LINKER_FLAGS
+    "${CMAKE_EXE_LINKER_FLAGS} --sysroot=${ROOTFS_ARM}"
+    CACHE INTERNAL "" FORCE)
+
+set(CMAKE_FIND_ROOT_PATH ${ROOTFS_ARM})
+# search for programs in the build host directories
+SET(CMAKE_FIND_ROOT_PATH_MODE_PROGRAM NEVER)
+# for libraries and headers in the target directories
+SET(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY)
+SET(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)
+SET(CMAKE_FIND_ROOT_PATH_MODE_PACKAGE ONLY)