一个完整的cmake+clang+llvm编译链接hello-world过程

偏执的太偏执、 2022-03-22 14:17 114阅读 0赞

相信目前使用clang+llvm大有人在，我的系统ubuntu18.04前段时间刚安装了不少软件，习惯性的也会装上gcc/g++和clang/clang++，关于如何在两个编译器之间切换这里不再赘述，可能参考下面的链接：  
[Switching between GCC and Clang/LLVM using CMake][Switching between GCC and Clang_LLVM using CMake]

写这个贴子是因为clang/clang++在网上大都没有一个完整的例子，大部分讲完clang就完事了，后面的链接部分语焉不详，所以这里给出一个完整的hello-world记录。

## 源码 ##

main.c

#include <stdio.h>
    
    int main() {
    	printf("Hello World.\n");
    	
    	return 0;
    }

CMakeLists.txt  
(参考：[https://releases.llvm.org/5.0.0/docs/CMake.html][https_releases.llvm.org_5.0.0_docs_CMake.html] )  
(参考：[https://llvm.org/docs/CMake.html][https_llvm.org_docs_CMake.html])

cmake_minimum_required(VERSION 3.7.1)
    
    project(hello-world)
    
    find_package(LLVM REQUIRED CONFIG)
    
    set(SOURCE_FILES main.c)
    
    message(STATUS "This is BINARY dir " ${PROJECT_BINARY_DIR})
    message(STATUS "This is SOURCE dir " ${PROJECT_SOURCE_DIR})
    message(STATUS "Found LLVM ${LLVM_PACKAGE_VERSION}")
    message(STATUS "Using LLVMConfig.cmake in: ${LLVM_DIR}")
    
    # Set your project compile flags.
    # E.g. if using the C++ header files
    # you will need to enable C++11 support
    # for your compiler.
    
    include_directories(${LLVM_INCLUDE_DIRS})
    add_definitions(${LLVM_DEFINITIONS})
    
    # Now build our tools
    add_executable(hello-world ${SOURCE_FILES})
    
    
    # Find the libraries that correspond to the LLVM components
    # that we wish to use
    llvm_map_components_to_libnames(llvm_libs support core irreader)
    
    # Link against LLVM libraries
    target_link_libraries(hello-world ${llvm_libs})

linux.toolchain.cmake

cmake_minimum_required( VERSION 2.6.3 )
    set(CMAKE_SYSTEM_NAME Linux )
    
    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")

## 编译生成 ##

这个其实就两条命令：  
$ cmake  -DCMAKE\_TOOLCHAIN\_FILE=./linux.toolchain.cmake  .  
$ make VERBOSE=1  
VERBOSE是因为要输出更多的信息（毕竟是在学习嘛），可以看到链接的详细情况。

$ cmake  -DCMAKE_TOOLCHAIN_FILE=./linux.toolchain.cmake  .
    -- The C compiler identification is Clang 6.0.0
    -- The CXX compiler identification is Clang 6.0.0
    -- Check for working C compiler: /usr/bin/clang
    -- Check for working C compiler: /usr/bin/clang -- works
    -- Detecting C compiler ABI info
    -- Detecting C compiler ABI info - done
    -- Detecting C compile features
    -- Detecting C compile features - done
    -- Check for working CXX compiler: /usr/bin/clang++
    -- Check for working CXX compiler: /usr/bin/clang++ -- works
    -- Detecting CXX compiler ABI info
    -- Detecting CXX compiler ABI info - done
    -- Detecting CXX compile features
    -- Detecting CXX compile features - done
    -- This is BINARY dir /home/matthew/devc/cmake/hello-world
    -- This is SOURCE dir /home/matthew/devc/cmake/hello-world
    -- Found LLVM 6.0.0
    -- Using LLVMConfig.cmake in: /usr/lib/llvm-6.0/cmake
    -- Configuring done
    -- Generating done
    -- Build files have been written to: /home/matthew/devc/cmake/hello-world
    
    $ make VERBOSE=1
    /usr/bin/cmake -H/home/matthew/devc/cmake/hello-world -B/home/matthew/devc/cmake/hello-world --check-build-system CMakeFiles/Makefile.cmake 0
    /usr/bin/cmake -E cmake_progress_start /home/matthew/devc/cmake/hello-world/CMakeFiles /home/matthew/devc/cmake/hello-world/CMakeFiles/progress.marks
    make -f CMakeFiles/Makefile2 all
    make[1]: 进入目录“/home/matthew/devc/cmake/hello-world”
    make -f CMakeFiles/hello-world.dir/build.make CMakeFiles/hello-world.dir/depend
    make[2]: 进入目录“/home/matthew/devc/cmake/hello-world”
    cd /home/matthew/devc/cmake/hello-world && /usr/bin/cmake -E cmake_depends "Unix Makefiles" 
    /home/matthew/devc/cmake/hello-world /home/matthew/devc/cmake/hello-world 
    /home/matthew/devc/cmake/hello-world /home/matthew/devc/cmake/hello-world 
    /home/matthew/devc/cmake/hello-world/CMakeFiles/hello-world.dir/DependInfo.cmake --color=
    make[2]: 离开目录“/home/matthew/devc/cmake/hello-world”
    make -f CMakeFiles/hello-world.dir/build.make CMakeFiles/hello-world.dir/build
    make[2]: 进入目录“/home/matthew/devc/cmake/hello-world”
    [ 50%] Linking CXX executable hello-world
    /usr/bin/cmake -E cmake_link_script CMakeFiles/hello-world.dir/link.txt --verbose=1
    /usr/bin/clang++     CMakeFiles/hello-world.dir/main.c.o  -o hello-world 
    /usr/lib/llvm-6.0/lib/libLLVMSupport.a /usr/lib/llvm-6.0/lib/libLLVMCore.a 
    /usr/lib/llvm-6.0/lib/libLLVMIRReader.a /usr/lib/llvm-6.0/lib/libLLVMAsmParser.a 
    /usr/lib/llvm-6.0/lib/libLLVMBitReader.a /usr/lib/llvm-6.0/lib/libLLVMCore.a 
    /usr/lib/llvm-6.0/lib/libLLVMBinaryFormat.a /usr/lib/llvm-6.0/lib/libLLVMSupport.a 
    -lz -lrt -ldl -ltinfo -lpthread -lm /usr/lib/llvm-6.0/lib/libLLVMDemangle.a 
    make[2]: 离开目录“/home/matthew/devc/cmake/hello-world”
    [100%] Built target hello-world
    make[1]: 离开目录“/home/matthew/devc/cmake/hello-world”
    /usr/bin/cmake -E cmake_progress_start /home/matthew/devc/cmake/hello-world/CMakeFiles 0

注意，如果不在当前目录下，则需要根据实际情况设置目录，如

export  CURRENT_SCRIPT_DIR=/home/matthew/devc/cmake/hello-world
    cmake  -DCMAKE_TOOLCHAIN_FILE=${CURRENT_SCRIPT_DIR}/linux.toolchain.cmake  .

## 关于LLVM宏定义 ##

LLVM相关的宏定义都在文件LLVMConfig.cmake中，一般情况下默认的路径如下所示  
 /usr/lib/llvm-6.0/cmake/LLVMConfig.cmake

如果你仔细阅读一下就会发现，LLVM\_INCLUDE\_DIRS和LLVM\_INCLUDE\_DIR是完全一样的，如下，  
set(LLVM\_INSTALL\_PREFIX "/usr/lib/llvm-6.0")  
......  
set(LLVM\_INCLUDE\_DIRS "$\{LLVM\_INSTALL\_PREFIX\}/include")  
set(LLVM\_LIBRARY\_DIRS "$\{LLVM\_INSTALL\_PREFIX\}/lib$\{LLVM\_LIBDIR\_SUFFIX\}")  
\# These variables are duplicated, but they must match the LLVM variables of the  
\# same name. The variables ending in "S" could some day become lists, and are  
\# preserved for convention and compatibility.  
set(LLVM\_INCLUDE\_DIR "$\{LLVM\_INSTALL\_PREFIX\}/include")  
set(LLVM\_LIBRARY\_DIR "$\{LLVM\_INSTALL\_PREFIX\}/lib$\{LLVM\_LIBDIR\_SUFFIX\}")

## 参考资料 ##

下面是一些写得比较好的贴子或文档网址，记录一下，  
[https://blog.csdn.net/dashuniuniu/article/details/50385528][https_blog.csdn.net_dashuniuniu_article_details_50385528]  
[https://www.ibm.com/developerworks/cn/opensource/os-cn-clang/][https_www.ibm.com_developerworks_cn_opensource_os-cn-clang]  
[https://llvm.org/pubs/][https_llvm.org_pubs]

[Switching between GCC and Clang_LLVM using CMake]: https://stackoverflow.com/questions/7031126/switching-between-gcc-and-clang-llvm-using-cmake
[https_releases.llvm.org_5.0.0_docs_CMake.html]: https://releases.llvm.org/5.0.0/docs/CMake.html
[https_llvm.org_docs_CMake.html]: https://llvm.org/docs/CMake.html
[https_blog.csdn.net_dashuniuniu_article_details_50385528]: https://blog.csdn.net/dashuniuniu/article/details/50385528
[https_www.ibm.com_developerworks_cn_opensource_os-cn-clang]: https://www.ibm.com/developerworks/cn/opensource/os-cn-clang/
[https_llvm.org_pubs]: https://llvm.org/pubs/