参数化自定义 CMake 工具链

Question

我正在编写用于交叉编译的 CMake 工具链文件。

我有几个工具链，它们略有不同。我想为 cmake 创建一个描述所有工具链的文件，并让用户从命令行指定它们：cmake -DCMAKE_TOOLCHAIN_FILE=/path/to/toolchain.cmake -DTOOLCHAIN_NAME=<name>

不过，好像TOOLCHAIN_NAME有时会变成空串。

这里是工具链文件的例子：

set(tools /opt/toolchains/Custom/toolchains/toolchain)
set(sdk   /opt/toolchains/Custom/platforms/)

message(STATUS "toolchain_name ${TOOLCHAIN_NAME}")
if(NOT TOOLCHAIN_NAME) 
    message(SEND_ERROR "Please specify toolchain name in -DTOOLCHAIN_NAME parameter")
endif()

set(CMAKE_SYSTEM_NAME Generic)
set(CMAKE_SYSTEM_PROCESSOR ARM)

# further processing

然后调用CMake:

mkdir build
cd build
cmake .. -DCMAKE_TOOLCHAIN_FILE=../cmake/toolchain.cmake -DTOOLCHAIN_NAME=proc-os-gnueabi-gcc_6_3

并得到以下错误输出：

-- toolchain name proc-os-gnueabi-gcc_6_3
-- toolchain name proc-os-gnueabi-gcc_6_3
-- The C compiler identification is GNU 6.3.1
-- The CXX compiler identification is GNU 6.3.1
-- Check for working C compiler: /opt/toolchains/.../bin/arm-os-gnueabi-gcc
CMake Error at /home/user/project/cmake/toolchain.cmake:59 (message):
  Please specify toolchain name in -DTOOLCHAIN_NAME parameter

Call Stack (most recent call first):
  /home/user/project/build/CMakeFiles/3.15.4/CMakeSystem.cmake:6 (include)
  /home/user/project/build/CMakeFiles/CMakeTmp/CMakeLists.txt:2 (project)


CMake Error at /usr/local/share/cmake-3.15/Modules/CMakeTestCCompiler.cmake:44 (try_compile):
  Failed to configure test project build system.
Call Stack (most recent call first):
  CMakeLists.txt:15 (project)


-- Configuring incomplete, errors occurred!
See also "/home/user/project/build/CMakeFiles/CMakeOutput.log".
See also "/home/user/project/build/CMakeFiles/CMakeError.log".

CMakeOutput.log 和 CMakeError.log 包含消息，说编译器没有找到一些库。

如果我打开生成的文件 /home/user/project/build/CMakeFiles/3.15.4/CMakeSystem.cmake 我可以看到以下内容

set(CMAKE_HOST_SYSTEM "Linux-4.2.0-27-generic")
set(CMAKE_HOST_SYSTEM_NAME "Linux")
set(CMAKE_HOST_SYSTEM_VERSION "4.2.0-27-generic")
set(CMAKE_HOST_SYSTEM_PROCESSOR "x86_64")

include("/home/user/project/cmake/toolchain.cmake")

set(CMAKE_SYSTEM "Generic")
set(CMAKE_SYSTEM_NAME "Generic")
set(CMAKE_SYSTEM_VERSION "")
set(CMAKE_SYSTEM_PROCESSOR "ARM")

set(CMAKE_CROSSCOMPILING "TRUE")

set(CMAKE_SYSTEM_LOADED 1)

根据 CMake 手册，其 -D 参数用于指定缓存条目。

我从上面的输出中得出结论，CMake 至少处理了 3 次提供的工具链文件。前两次有适当的缓存条目，而在第三次运行它们不存在。

那么，如何避免工具链文件的代码重复？

更新。阅读后，我尝试了几种 CMake 命令行参数排列：在工具链之后但在选项之前指定源路径，在选项之后指定它，使用 -S 和 [=19 明确指定源路径和构建路径=] 选项。没有任何帮助。

Answer 1

I conclude from the output above that supplied toolchain file is processed by CMake at least 3 times. First two times there were proper cache entries, and at the third run they were absent.

是的，这是非常好的观察。从技术上讲，只有 project() 调用中的第一个工具链调用才能保证看到缓存条目（使用 -D 参数创建 cmake 或使用 set() 命令在 project()呼叫）。

在不同工具链调用之间传递缓存条目的一种方法是将它们存储在环境变量:

中

下面的示例使用 MY_TOOLCHAIN_NAME 环境变量作为 TOOLCHAIN_NAME CMake 变量的存储。

if(DEFINED ENV{MY_TOOLCHAIN_NAME})
    # Environment variable is set.
    if (TOOLCHAIN_NAME)
        # CMake variable is set too.
        # It is up to your which one to use.
        # Uncomment line below for prefer environment variable to CMake one.
        # set(TOOLCHAIN_NAME $ENV{MY_TOOLCHAIN_NAME})
    else ()
        # CMake variable is not set. Use environment one.
        set(TOOLCHAIN_NAME $ENV{MY_TOOLCHAIN_NAME})
    endif()
else()
    # Environment variable is not set.
    if (TOOLCHAIN_NAME)
        # But CMake variable is set.
        # Store it into the environment and use it.
        set(ENV{MY_TOOLCHAIN_NAME} ${TOOLCHAIN_NAME})
    else()
        # Neither environment nor CMake variable is set.
        message(SEND_ERROR "Please specify toolchain name in -DTOOLCHAIN_NAME parameter")
    endif()
endif()

如果您有多个“调整”变量，您可以为上述所有步骤编写一个宏，然后为您需要的每个变量应用（调用）该宏。

参数化自定义 CMake 工具链

Parameterizing custom CMake toolchain

c++

cmake

cross-compiling