CoreCLR登陆GitHub之后，体验CoreCLR首当其冲的方式就是在自己的电脑上编译它，昨天分别在Windows与Linux上成功编译了CoreCLR，详见：
Windows与Linux上编译成功之后，有一个挡不住的冲动——在Mac上编译CoreCLR。虽然微软目前优先考虑的是Windows与Linux两个平台，CoreCLR的编译暂时不支持Mac OS X，但我最期待的却是在Mac OS X上编译CoreCLR，而且编译CoreCLR所需要的CMake与LLVM在Mac OS X上都有，尝试一下是必须的。
于是，心动不如行动，开始了Mac OS X编译CoreCLR之旅。
Build操作步骤如下：
1）签出github上的CoreCLR代码库： git clone https://github.com/dotnet/coreclr.git
2）安装cmake： brew install cmake
3）运行build命令： sh build.sh
3）build结果-失败，错误信息如下：
Unable to locate llvm-ar Failed to generate native component build project!
错误信息显示找不到llvm-ar命令。
运行命令 clang --version ，确认LLVM 3.5已安装：
Apple LLVM version 6.0 (clang-600.0.56) (based on LLVM 3.5svn)
运行命令 ls /usr/bin/llvm* ，的确没有llvm-ar：
/usr/bin/llvm-g++ /usr/bin/llvm-gcc
后来发现原来藏在 /usr/local/opt/llvm/bin/ 文件夹中：
ls /usr/local/opt/llvm/bin/llvm-ar /usr/local/opt/llvm/bin/llvm-ar
但环境变量$PATH中没有这个路径，于是加上这个路径：
export PATH=/usr/local/opt/llvm/bin:$PATH
添加之后，继续build，“Unable to locate llvm-ar”错误消失。
但出现了新的错误：
-- The C compiler identification is AppleClang 6.0.0.6000056 -- The CXX compiler identification is AppleClang 6.0.0.6000056 -- 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 -- 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 CMake Error at CMakeLists.txt:317 (message): Not Implemented!
查看CMakeLists.txt中的代码：
if (IS_64BIT_BUILD EQUAL 1)
if (CLR_CMAKE_PLATFORM_UNIX_TARGET_AMD64)
add_definitions(-DDBG_TARGET_AMD64_UNIX)
endif (CLR_CMAKE_PLATFORM_UNIX_TARGET_AMD64)
add_definitions(-D_TARGET_AMD64_=1)
add_definitions(-DDBG_TARGET_AMD64)
else (IS_64BIT_BUILD EQUAL 1)
# TODO: Support this
message(FATAL_ERROR "Not Implemented!") #line 317
endif (IS_64BIT_BUILD EQUAL 1)
第317代码是 message(FATAL_ERROR "Not Implemented!") 。分析这段if代码块，可以知道当操作系统是Mac OS X时，IS_64BIT_BUILD的值不为1，如果将之设置为1就可以避开这个错误。
于是顺藤摸瓜，在CMakeLists.txt的第128行找到了设置IS_64BIT_BUILD的代码：
elseif (CLR_CMAKE_PLATFORM_UNIX)
# Set flag to indicate if this will be a 64bit Linux build
if(CMAKE_SYSTEM_PROCESSOR STREQUAL x86_64)
set(IS_64BIT_BUILD 1)
endif (CMAKE_SYSTEM_PROCESSOR STREQUAL x86_64)
当CLR_CMAKE_PLATFORM_UNIX为true的时候，会将IS_64BIT_BUILD的值设置为1。
继续顺藤摸瓜，在CMakeLists.txt的第7行找到了设置CLR_CMAKE_PLATFORM_UNIX的代码：
if(CMAKE_SYSTEM_NAME STREQUAL Linux)
set(CLR_CMAKE_PLATFORM_UNIX 1)
set(CLR_CMAKE_PLATFORM_UNIX_TARGET_AMD64 1)
endif(CMAKE_SYSTEM_NAME STREQUAL Linux)
然后依葫芦画瓢，添加了针对Mac OS X的代码：
# Mac OS X
if(CMAKE_SYSTEM_NAME STREQUAL Darwin)
set(CLR_CMAKE_PLATFORM_UNIX 1)
set(CLR_CMAKE_PLATFORM_UNIX_TARGET_AMD64 1)
endif(CMAKE_SYSTEM_NAME STREQUAL Darwin)
然后运行./build.sh编译CoreCLR，终于将build.sh跑起来了。虽然也有一些报错，但是build的执行没有中断：
Commencing CoreCLR Repo build
Checking pre-requisites...
Commencing build of native components for amd64/debug
Invoking cmake with arguments: /git/dotnet/coreclr DEBUG
Detected Linux x86_64
-- Configuring done
CMake Warning (dev):
Policy CMP0042 is not set: MACOSX_RPATH is enabled by default. Run "cmake
--help-policy CMP0042" for policy details. Use the cmake_policy command to
set the policy and suppress this warning.
MACOSX_RPATH is not specified for the following targets:
coreclr
mscordaccore
This warning is for project developers. Use -Wno-dev to suppress it.
-- Generating done
-- Build files have been written to: /git/dotnet/coreclr/binaries/CMake
Executing make
./build.sh: line 84: nproc: command not found
[ 0%] Building C object src/pal/tools/cppmunge/CMakeFiles/cppmunge.dir/cppmunge.c.o
[ 1%] [ 1%] Built target palrt
[ 1%] Built target mdhotdata_full
Built target gcinfo
/git/dotnet/coreclr/src/pal/tools/cppmunge/cppmunge.c:38:10: fatal error: ‘linux/limits.h‘ file not found
#include <linux/limits.h>
^
[ 1%] [ 1%] Built target ildbsymlib
Built target dbgutil
[ 2%] Built target corguids
[ 3%] Built target ceefgen
满怀期望地等待着build的结果。。。
但是在build过程中，MacBook的CPU风扇突然呼呼作响，接着OS X系统停止响应，只能强制关机。
开机后再尝试，在build过程中依然会让Mac挂掉。接着进行多次尝试，只要build，Mac必挂。
Mac OS X上编译CoreCLR之旅因为这个暂时无法解决的问题而中断。
虽然这次尝试失败了，但是在Mac OS X上编译CoreCLR的痴心不改，在Mac OS X上开发.NET程序的期待不变！