在CMake中设置SDK交叉编译到OSX

Question

我正在使用CMake从Linux交叉编译到OSX。为此，我使用了一个工具链文件，因此调用如下:

cmake -G 'Unix Makefiles' -DCMAKE_TOOLCHAIN_FILE=./cmake/toolchains/c.apple.universal.cmake .

工具链文件如下所示:

SET(CMAKE_SYSTEM_NAME Darwin)
SET(CMAKE_SYSTEM_PROCESSOR universal)
# set compilers...
INCLUDE("${CMAKE_CURRENT_LIST_DIR}/c.apple.common.cmake")

另一个:

INCLUDE("${CMAKE_CURRENT_LIST_DIR}/../Modules/CMakeMacroSetCCache.cmake")
# specify the cross compiler
SET_CCACHE(CMAKE_C_COMPILER i686-apple-darwin10-gcc)
SET_CCACHE(CMAKE_CXX_COMPILER i686-apple-darwin10-g++)
SET(CMAKE_RANLIB i686-apple-darwin10-ranlib CACHE STRING "" FORCE)
SET(CMAKE_LIPO i686-apple-darwin10-lipo CACHE STRING "" FORCE)
SET(OSX104_SDK "/usr/lib/apple/SDKs/MacOSX10.4.sdk")
SET(OSX105_SDK "/usr/lib/apple/SDKs/MacOSX10.5.sdk")
# set SDK
SET(CMAKE_OSX_DEPLOYMENT_TARGET )
IF(EXISTS ${OSX104_SDK})
    SET(CMAKE_OSX_SYSROOT ${OSX104_SDK})
ELSEIF(EXISTS ${OSX105_SDK})
    SET(CMAKE_OSX_SYSROOT ${OSX105_SDK})
ELSE()
    MESSAGE(FATAL_ERROR "No OSX SDK found!")
ENDIF()
MESSAGE(STATUS "Using OSX SDK at ${CMAKE_OSX_SYSROOT}")
SET(CMAKE_PREFIX_PATH ${CMAKE_OSX_SYSROOT})
SET(CMAKE_FIND_ROOT_PATH ${CMAKE_PREFIX_PATH})
SET(BOOST_ROOT ${CMAKE_PREFIX_PATH})
# 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)

这个工作到目前为止，但不知何故CMake重置CMAKE_OSX_SYSROOT在某些点。我得到的输出是:

-- Set CMAKE_C_COMPILER to /usr/lib/ccache-lipo/i686-apple-darwin10-gcc
-- Set CMAKE_CXX_COMPILER to /usr/lib/ccache-lipo/i686-apple-darwin10-g++
-- Using OSX SDK at /usr/lib/apple/SDKs/MacOSX10.5.sdk
-- Set CMAKE_C_COMPILER to /usr/lib/ccache-lipo/i686-apple-darwin10-gcc
-- Set CMAKE_CXX_COMPILER to /usr/lib/ccache-lipo/i686-apple-darwin10-g++
-- Using OSX SDK at /usr/lib/apple/SDKs/MacOSX10.5.sdk
-- The C compiler identification is GNU
-- The CXX compiler identification is GNU
-- Checking whether C compiler has -isysroot
-- Checking whether C compiler has -isysroot - yes
-- Checking whether C compiler supports OSX deployment target flag
-- Checking whether C compiler supports OSX deployment target flag - yes
-- Check for working C compiler: /usr/lib/ccache-lipo/i686-apple-darwin10-gcc
-- Check for working C compiler: /usr/lib/ccache-lipo/i686-apple-darwin10-gcc -- works
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Checking whether CXX compiler has -isysroot
-- Checking whether CXX compiler has -isysroot - yes
-- Checking whether CXX compiler supports OSX deployment target flag
-- Checking whether CXX compiler supports OSX deployment target flag - yes
-- Check for working CXX compiler: /usr/lib/ccache-lipo/i686-apple-darwin10-g++
-- Check for working CXX compiler: /usr/lib/ccache-lipo/i686-apple-darwin10-g++ -- works
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Used Toolchain definition file '/srv/jenkins/.../cmake/toolchains/c.apple.universal.cmake'
-- Configuring for cross-compiling to Darwin on universal
-- Using platform config cmake/darwin.cmake
-- Checking /Developer/SDKs/MacOSX.sdk/usr/lib/libSystem.B.dylib for possible architectures

最后3行来自CMakeList.txt。使用了正确的工具链文件(这只是一条消息)，SYSTEM_NAME和SYSTEM_PROCESSOR设置正确，但OSX SDK错误。相应的CMake代码来自一个宏，如果之前没有设置CMAKE_OSX_ARCHITECTURES(这里就是这种情况)，该宏将设置CMAKE_OSX_ARCHITECTURES。这一行是:

MESSAGE(STATUS "Checking ${CMAKE_OSX_SYSROOT}/usr/lib/libSystem.B.dylib for possible architectures")

我在这里错误地使用CMake吗?为什么CMake重置OSX_SYSROOT?根据http://www.cmake.org/cmake/help/v3.0/variable/CMAKE_OSX_SYSROOT.html，它也应该影响FIND*命令，但我需要设置CMAKE_FIND_ROOT_PATH为它的工作。

真奇怪，昨天还管用。清理整个构建目录(我确信我昨天也做了)并重新运行CMake现在重置CMAKE_OSX_SYSROOT。

如果在包含结束宏执行之前调用PROJECT，则显示错误的系统根。

Answer 1

我找到的解决方案是将变量设置到缓存中。通过这种方式，它在CMake处理期间"存活":

SET(CMAKE_OSX_SYSROOT ${CMAKE_OSX_SYSROOT} CACHE PATH "..." FORCE)