一个完整的CMake+ＯpenMPI编译链接hello-world过程

电玩女神 2022-03-21 03:37 141阅读 0赞

前面写了一个关于《[一个完整的cmake+clang+llvm编译链接hello-world过程][cmake_clang_llvm_hello-world]》，感觉写这个的时候有点多余，因为大多数都是依葫葫芦画瓢，不过刚刚碰到一些MPI的问题，在网上找了一圈，发现太多关于MPI的误人子弟的贴子（我想主要原因可能是因为这些帖子太老了，不适用，软件都已经更新了好几代了），所以在这里写个简单的hello-world澄清一下。

比如MPI入门级的大量的报错，  
Linking Error: undefined reference to \`MPI\_Init'  
网上多数贴子的理由五花八门，比如说要用mpi++而不是mpicc啦，gcc语法不对啦，其实最根本的原因是因为没有找到链接MPI的库文件，下面我们详细说明，知其然，知其所以然。

## 源码 ##

mpich学习的源码部分可参考  
[https://github.com/wesleykendall/mpitutorial][https_github.com_wesleykendall_mpitutorial]  
（克隆命令：git clone https://github.com/wesleykendall/mpitutorial.git）  
我取其中最简单那个做个示范，我安装的是OpenMPI，这主要是因为我用到的项目大多依赖OpenMPI而不是MPICH。

内容如下，

**mpi-hello-world / 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")

**mpi-hello-world / CMakeLists.txt**

cmake_minimum_required(VERSION 3.7.1)
    project(hello)
    add_subdirectory(src)

**mpi-hello-world / src / CMakeLists.txt**

cmake_minimum_required(VERSION 3.7.1)
    
    project(hello-world)
    
    find_package(LLVM REQUIRED CONFIG)
    find_package(MPI REQUIRED)
    
    
    set(SOURCE_FILES mpi_hello_world.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}")
    message(STATUS "Using LLVM_INCLUDE_DIRS: ${LLVM_INCLUDE_DIRS}")
    message(STATUS "Using LLVM_DEFINITIONS: ${LLVM_DEFINITIONS}")
    message(STATUS "Using MPI_INCLUDE_PATH: ${MPI_INCLUDE_PATH}")
    message(STATUS "Using MPI_C_LIBRARIES: ${MPI_C_LIBRARIES}")
    
    #/usr/lib/x86_64-linux-gnu/openmpi/include
    include_directories(SYSTEM ${MPI_INCLUDE_PATH})
    include_directories(${LLVM_INCLUDE_DIRS} )
    add_definitions(${LLVM_DEFINITIONS})
    
    add_executable(hello ${SOURCE_FILES})
    
    llvm_map_components_to_libnames(llvm_libs support core irreader)
    
    target_link_libraries(hello ${llvm_libs} ${MPI_C_LIBRARIES})

**mpi-hello-world / src / mpi-hello-world.c**

// Author: Wes Kendall
    // Copyright 2011 www.mpitutorial.com
    // This code is provided freely with the tutorials on mpitutorial.com. Feel
    // free to modify it for your own use. Any distribution of the code must
    // either provide a link to www.mpitutorial.com or keep this header intact.
    //
    // An intro MPI hello world program that uses MPI_Init, MPI_Comm_size,
    // MPI_Comm_rank, MPI_Finalize, and MPI_Get_processor_name.
    //
    #include <mpi.h>
    #include <stdio.h>
    
    int main(int argc, char** argv) {
      // Initialize the MPI environment. The two arguments to MPI Init are not
      // currently used by MPI implementations, but are there in case future
      // implementations might need the arguments.
      MPI_Init(NULL, NULL);
    
      // Get the number of processes
      int world_size;
      MPI_Comm_size(MPI_COMM_WORLD, &world_size);
    
      // Get the rank of the process
      int world_rank;
      MPI_Comm_rank(MPI_COMM_WORLD, &world_rank);
    
      // Get the name of the processor
      char processor_name[MPI_MAX_PROCESSOR_NAME];
      int name_len;
      MPI_Get_processor_name(processor_name, &name_len);
    
      // Print off a hello world message
      printf("Hello world from processor %s, rank %d out of %d processors\n",
             processor_name, world_rank, world_size);
    
      // Finalize the MPI environment. No more MPI calls can be made after this
      MPI_Finalize();
    }

## 编译源码并运行 ##

注意我在CMakeLists.txt中加了相当多的调试信息，切换到build目录下后，执行，

$ cmake  -DCMAKE_TOOLCHAIN_FILE=../linux.toolchain.cmake  ..
    $ make VERBOSE=1

就可得到详细的运行信息，如下

$ 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
    -- Found MPI_C: /usr/lib/x86_64-linux-gnu/openmpi/lib/libmpi.so (found version "3.1") 
    -- Found MPI_CXX: /usr/lib/x86_64-linux-gnu/openmpi/lib/libmpi_cxx.so (found version "3.1") 
    -- Found MPI: TRUE (found version "3.1")  
    -- This is BINARY dir /home/user01/devc/mpitutorial/tutorials/mpi-hello-world/build/src
    -- This is SOURCE dir /home/user01/devc/mpitutorial/tutorials/mpi-hello-world/src
    -- Found LLVM 6.0.0
    -- Using LLVMConfig.cmake in: /usr/lib/llvm-6.0/cmake
    -- Using LLVM_INCLUDE_DIRS: /usr/lib/llvm-6.0/include
    -- Using LLVM_DEFINITIONS: -D_GNU_SOURCE -D__STDC_CONSTANT_MACROS 
    -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS
    -- Using MPI_INCLUDE_PATH: /usr/lib/x86_64-linux-gnu/openmpi/include/openmpi;
    /usr/lib/x86_64-linux-gnu/openmpi/include/openmpi/opal/mca/event/libevent2022/libevent;
    /usr/lib/x86_64-linux-gnu/openmpi/include/openmpi/opal/mca/event/libevent2022/libevent/include;
    /usr/lib/x86_64-linux-gnu/openmpi/include
    -- Using MPI_C_LIBRARIES: /usr/lib/x86_64-linux-gnu/openmpi/lib/libmpi.so
    -- Configuring done
    -- Generating done
    -- Build files have been written to: /home/user01/devc/mpitutorial/tutorials/mpi-hello-world/build
    
    
    $ make VERBOSE=1
    /usr/bin/cmake -H/home/user01/devc/mpitutorial/tutorials/mpi-hello-world 
    -B/home/user01/devc/mpitutorial/tutorials/mpi-hello-world/build 
    --check-build-system CMakeFiles/Makefile.cmake 0
    /usr/bin/cmake -E cmake_progress_start 
    /home/user01/devc/mpitutorial/tutorials/mpi-hello-world/build/CMakeFiles 
    /home/user01/devc/mpitutorial/tutorials/mpi-hello-world/build/CMakeFiles/progress.marks
    make -f CMakeFiles/Makefile2 all
    ......
    Scanning dependencies of target hello
    ......
    make[2]: 离开目录“/home/user01/devc/mpitutorial/tutorials/mpi-hello-world/build”
    [100%] Built target hello
    make[1]: 离开目录“/home/user01/devc/mpitutorial/tutorials/mpi-hello-world/build”
    /usr/bin/cmake -E cmake_progress_start 
    /home/user01/devc/mpitutorial/tutorials/mpi-hello-world/build/CMakeFiles 0

最后生成的可执行文件在 **mpi-hello-world / build / src / hello。**

### 关于MPI宏定义: MPI\_C\_LIBRARIES和MPI\_C\_INCLUDE\_PATH ###

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

CMake中的module findMPI.cmake在如下路径，  
/usr/share/cmake-3.10/Modules    
/usr/share/cmake-3.13/Modules  
如果你对findMPI感兴趣，可以详细阅读一下源码，其中有定义MPI\_C\_LIBRARIES和MPI\_C\_INCLUDE\_PATH  
注意：MPI\_C\_INCLUDE\_PATH和MPI\_INCLUDE\_PATH的效力是一样的，这一点cmake官方文档中有详细说明，可参考：  
[https://cmake.org/cmake/help/v3.13/module/FindMPI.html][https_cmake.org_cmake_help_v3.13_module_FindMPI.html]  
链接库在这里target\_link\_libraries(hello $\{llvm\_libs\}　$\{ MPI\_C\_LIBRARIES\})从调试输出部分也可以看到，MPI\_C\_LIBRARIES相当于链接到了这个库 /usr/lib/x86\_64-linux-gnu/openmpi/lib/libmpi.so

## 总结 ##

总结一下MPI编程的基本步骤

step.1: 对于 MPI ，首先你必须先找到MPI  
find\_package(MPI) \#必需的

step.2: 然后将其添加的头文件到您的搜索路径  
include\_directories(SYSTEM $ \{\} MPI\_INCLUDE\_PATH）

step.3:和最后链接程序  
target\_link\_libraries(target $\{MPI\_C\_LIBRARIES\})

## 参考资料 ##

[https://cmake.org/cmake/help/v3.13/module/FindMPI.html][https_cmake.org_cmake_help_v3.13_module_FindMPI.html]  
[https://github.com/wesleykendall/mpitutorial][https_github.com_wesleykendall_mpitutorial]

[cmake_clang_llvm_hello-world]: https://blog.csdn.net/tanmx219/article/details/86681167
[https_github.com_wesleykendall_mpitutorial]: https://github.com/wesleykendall/mpitutorial
[https_cmake.org_cmake_help_v3.13_module_FindMPI.html]: https://cmake.org/cmake/help/v3.13/module/FindMPI.html