使用CMake在GCC和Clang / LLVM之间切换 [英] Switching between GCC and Clang/LLVM using CMake

问题描述

我有一些项目使用CMake构建，我想要能够轻松地在使用GCC或Clang / LLVM之间切换编译它们。我相信（如果我错了，请纠正我）使用Clang我需要设置以下：

I have a number of projects built using CMake and I'd like to be able to easily switch between using GCC or Clang/LLVM to compile them. I believe (please correct me if I'm mistaken!) that to use Clang I need to set the following:

    SET (CMAKE_C_COMPILER             "/usr/bin/clang")
    SET (CMAKE_C_FLAGS                "-Wall -std=c99")
    SET (CMAKE_C_FLAGS_DEBUG          "-g")
    SET (CMAKE_C_FLAGS_MINSIZEREL     "-Os -DNDEBUG")
    SET (CMAKE_C_FLAGS_RELEASE        "-O4 -DNDEBUG")
    SET (CMAKE_C_FLAGS_RELWITHDEBINFO "-O2 -g")

    SET (CMAKE_CXX_COMPILER             "/usr/bin/clang++")
    SET (CMAKE_CXX_FLAGS                "-Wall")
    SET (CMAKE_CXX_FLAGS_DEBUG          "-g")
    SET (CMAKE_CXX_FLAGS_MINSIZEREL     "-Os -DNDEBUG")
    SET (CMAKE_CXX_FLAGS_RELEASE        "-O4 -DNDEBUG")
    SET (CMAKE_CXX_FLAGS_RELWITHDEBINFO "-O2 -g")

    SET (CMAKE_AR      "/usr/bin/llvm-ar")
    SET (CMAKE_LINKER  "/usr/bin/llvm-ld")
    SET (CMAKE_NM      "/usr/bin/llvm-nm")
    SET (CMAKE_OBJDUMP "/usr/bin/llvm-objdump")
    SET (CMAKE_RANLIB  "/usr/bin/llvm-ranlib")

有一个简单的方法，在这些和默认GCC变量，优选作为系统范围变化而不是项目特定（即，

Is there an easy way of switching between these and the default GCC variables, preferably as a system-wide change rather than project specific (i.e. not just adding them into a project's CMakeLists.txt)?

此外，是否需要使用 llvm - * 程序，而不是使用clang而不是gcc编译时的系统默认值？有什么区别？

Also, is it necessary to use the llvm-* programs rather than the system defaults when compiling using clang instead of gcc? What's the difference?

推荐答案

CMake尊重环境变量 CC code> CXX 检测到C和C ++编译器使用：

CMake honors the environment variables CC and CXX upon detecting the C and C++ compiler to use:

$ export CC=/usr/bin/clang
$ export CXX=/usr/bin/clang++
$ cmake ..
-- The C compiler identification is Clang
-- The CXX compiler identification is Clang

编译器特定标志可以通过将其放入系统范围的CMake文件并指向该 CMAKE_USER_MAKE_RULES_OVERRIDE 变量。使用以下内容创建文件〜/ ClangOverrides.txt ：

The compiler specific flags can be overridden by putting them into a system wide CMake file and pointing the CMAKE_USER_MAKE_RULES_OVERRIDE variable to it. Create a file ~/ClangOverrides.txt with the following contents:

SET (CMAKE_C_FLAGS_INIT                "-Wall -std=c99")
SET (CMAKE_C_FLAGS_DEBUG_INIT          "-g")
SET (CMAKE_C_FLAGS_MINSIZEREL_INIT     "-Os -DNDEBUG")
SET (CMAKE_C_FLAGS_RELEASE_INIT        "-O4 -DNDEBUG")
SET (CMAKE_C_FLAGS_RELWITHDEBINFO_INIT "-O2 -g")

SET (CMAKE_CXX_FLAGS_INIT                "-Wall")
SET (CMAKE_CXX_FLAGS_DEBUG_INIT          "-g")
SET (CMAKE_CXX_FLAGS_MINSIZEREL_INIT     "-Os -DNDEBUG")
SET (CMAKE_CXX_FLAGS_RELEASE_INIT        "-O4 -DNDEBUG")
SET (CMAKE_CXX_FLAGS_RELWITHDEBINFO_INIT "-O2 -g")

后缀_INIT将使CMake用给定的值初始化相应的 * _ FLAGS 变量。然后通过以下方式调用cmake：

The suffix _INIT will make CMake initialize the corresponding *_FLAGS variable with the given value. Then invoke cmake in the following way:

$ cmake -DCMAKE_USER_MAKE_RULES_OVERRIDE=~/ClangOverrides.txt ..

最后强制使用LLVM binutils，设置内部变量 _CMAKE_TOOLCHAIN_PREFIX 。此变量受到 CMakeFindBinUtils 模块的支持：

Finally to force the use of the LLVM binutils, set the internal variable _CMAKE_TOOLCHAIN_PREFIX. This variable is honored by the CMakeFindBinUtils module:

$ cmake -D_CMAKE_TOOLCHAIN_PREFIX=llvm- ..

将这一切放在一起你可以编写一个shell包装器来设置环境变量 CC 和 CXX ，然后使用上述变量覆盖调用cmake。

Putting this all together you can write a shell wrapper which sets up the environment variables CC and CXX and then invokes cmake with the mentioned variable overrides.

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