CentOS 7 如何安装llvm-project-10.0.0？

需要先升级gcc至7.5版本，详见CentOS 7如何编译安装升级gcc版本?一文

# 备份之前的yum .repo文件至 /tmp/repo_bak 目录
mkdir -p /tmp/repo_bak &&  cd /etc/yum.repo.d && /bin/mv ./*.repo /tmp/repo_bak

# 更换yum软件源为阿里云镜像源，执行脚本后一直全部回车即可
bash <(curl -sSL https://linuxmirrors.cn/main.sh)

# 使用阿里云镜像源安装编译依赖
yum install -y gcc gcc-c++ make cmake3 git zlib-devel ncurses-devel

# 声明新GCC相关的环境变量，注意此步必须执行，否则后续GCC编译无法调用7.5版本新的运行库
cat << 'EOF' >> ~/.bashrc
export PATH=/usr/local/bin:$PATH
export LD_LIBRARY_PATH=/usr/local/lib64:$LD_LIBRARY_PATH
export LIBRARY_PATH=/usr/local/lib64:$LIBRARY_PATH
export C_INCLUDE_PATH=/usr/local/include
export CPLUS_INCLUDE_PATH=/usr/local/include/c++/7.5.0
EOF
source ~/.bashrc

# 验证系统是否可以加载到 libstdc++.so.6 与 GLIBCXX_3.4.21，若无法加载需升级gcc至7.5版本
ldd $(which g++) ｜ grep libstdc++.so.6 => /usr/local/lib64/libstdc++.so.6
strings /usr/local/lib64/libstdc++.so.6 | grep GLIBCXX_3.4.21


cd /tmp
# 下载 LLVM 源码
wget https://github.com/llvm/llvm-project/releases/download/llvmorg-10.0.0/llvm-project-10.0.0.tar.xz
tar -xf llvm-project-10.0.0.tar.xz

# 注意：此处必须创建单独的构建目录，必须在非源码目录中构建（LLVM 禁止 in-source build）
mkdir -p /tmp/llvm-project-10.0.0/llvm-build
cd /tmp/llvm-project-10.0.0/llvm-build

# 运行 cmake3，在 build 目录中，指向 llvm 源码目录
cmake3 -G "Unix Makefiles" \
  -DCMAKE_C_COMPILER=/usr/local/bin/gcc \
  -DCMAKE_CXX_COMPILER=/usr/local/bin/g++ \
  -DCMAKE_BUILD_TYPE=Release \
  -DCMAKE_INSTALL_PREFIX=/opt/llvm-10 \
  -DLLVM_ENABLE_PROJECTS="clang" \
  -DLLVM_TARGETS_TO_BUILD="X86" \
  -DLLVM_ENABLE_TERMINFO=OFF \
  ../llvm

# 编译并安装，预计需要3小时左右
make -j1 VERBOSE=1
sudo make install

# 编译完成后验证 llvm-config
/opt/llvm-10/bin/llvm-config --version

# 声明 LLVM-10 工具链 环境变量
cat << 'EOF' >> ~/.bashrc
export PATH=/opt/llvm-10/bin:$PATH
export LD_LIBRARY_PATH=/opt/llvm-10/lib:$LD_LIBRARY_PATH
EOF
source ~/.bashrc

# 验证LLVM-10 工具链是否可以正常使用
clang --version
llvm-config --prefix

笔者安装踩坑过程：
1 执行cmake3 -G "Unix Makefiles" -DCMAKE_INSTALL_PREFIX=/opt/llvm-10 ../输出ERROR：

CMake Error: The source directory “/tmp/llvm-project-10.0.0” does not appear to contain CMakeLists.txt.
Specify --help for usage, or press the help button on the CMake GUI.

解决方案：cmake3构建要明确指定包含CMake构建系统核心配置文件的目录位置

llvm-project-10.0.0/
├── llvm  ✅ <- 需要在cmake3构建命令结尾明确指定这个目录寻找CMake构建系统的核心配置文件
│   ├── CMakeLists.txt  
│   └── ...
├── clang/
├── lld/
└── ...

改为为如下命令

cd /tmp
# 下载 LLVM 源码
wget https://github.com/llvm/llvm-project/releases/download/llvmorg-10.0.0/llvm-project-10.0.0.tar.xz
tar -xf llvm-project-10.0.0.tar.xz

# 注意：此处必须创建单独的构建目录，必须在非源码目录中构建（LLVM 禁止 in-source build）
mkdir -p /tmp/llvm-project-10.0.0/llvm-build
cd /tmp/llvm-project-10.0.0/llvm-build

cmake3 -G "Unix Makefiles" \
  -DCMAKE_C_COMPILER=/usr/local/bin/gcc \
  -DCMAKE_CXX_COMPILER=/usr/local/bin/g++ \
  -DCMAKE_BUILD_TYPE=Release \
  -DCMAKE_INSTALL_PREFIX=/opt/llvm-10 \
  -DLLVM_ENABLE_PROJECTS="clang" \
  -DLLVM_TARGETS_TO_BUILD="X86" \
  -DLLVM_ENABLE_TERMINFO=OFF \
  ../llvm #  ✅ <- 明确指定llvm目录，用于寻找CMake构建系统的核心配置文件

2 在/tmp/llvm-project-10.0.0/lllvm目录下cmake3 构建输出ERROR：

CMake Error at CMakeLists.txt:242 (message):
In-source builds are not allowed.

Please create a directory and run cmake from there, passing the path

to this source directory as the last argument.

This process created the file CMakeCache.txt’ and the directory
CMakeFiles’.

Please delete them.

– Configuring incomplete, errors occurred!
See also “/tmp/llvm-project-10.0.0/llvm/CMakeFiles/CMakeOutput.log”.

解决方案：LLVM 明确要求在单独的 build 目录中构建，禁止在源代码目录 llvm-project-10.0.0/llvm 中运行了 cmake3

3 执行make -j$(nproc)输出ERROR：

CMake Error at cmake/modules/CheckCompilerVersion.cmake:38 (message):
Host GCC version must be at least 5.1, your version is 4.8.5.
Call Stack (most recent call first):
cmake/modules/CheckCompilerVersion.cmake:48 (check_compiler_version)
cmake/config-ix.cmake:13 (include)
CMakeLists.txt:623 (include)

– Configuring incomplete, errors occurred!
See also “/tmp/llvm-project-10.0.0/build/CMakeFiles/CMakeOutput.log”.

解决方案：编译要求 GCC ≥ 5.1，但CentOS 7系统默认是 4.8.5，升级系统GCC版本至7.5，详见CentOS 7如何编译安装升级gcc版本?一文

4 执行make -j$(nproc)输出ERROR：
…/…/…/bin/llvm-tblgen: /lib64/libstdc++.so.6: version GLIBCXX_3.4.20’ not found (required by …/…/…/bin/llvm-tblgen)
…/…/…/bin/llvm-tblgen: /lib64/libstdc++.so.6: version CXXABI_1.3.9’ not found (required by …/…/…/bin/llvm-tblgen)
…/…/…/bin/llvm-tblgen: /lib64/libstdc++.so.6: version GLIBCXX_3.4.21’ not found (required by …/…/…/bin/llvm-tblgen)
make[2]: *** [include/llvm/IR/Attributes.inc] Error 1
make[2]: Leaving directory /home/tmp/llvm-project-10.0.0/llvm-build’
make[1]: *** [include/llvm/IR/CMakeFiles/intrinsics_gen.dir/all] Error 2
make[1]: Leaving directory /home/tmp/llvm-project-10.0.0/llvm-build’
make: *** [all] Error 2
解决方案：先声明环如下境变量，再将make -j$(nproc)并行编译改为make -j1 VERBOSE=1

# 声明新GCC相关的环境变量，注意此步必须执行，否则后续GCC编译无法调用7.5版本新的运行库
cat << 'EOF' >> ~/.bashrc
export PATH=/usr/local/bin:$PATH
export LD_LIBRARY_PATH=/usr/local/lib64:$LD_LIBRARY_PATH
export LIBRARY_PATH=/usr/local/lib64:$LIBRARY_PATH
export C_INCLUDE_PATH=/usr/local/include
export CPLUS_INCLUDE_PATH=/usr/local/include/c++/7.5.0
EOF
source ~/.bashrc

5 执行clang --version与 llvm-config --prefix输出ERROR：

clang: /lib64/libstdc++.so.6: version GLIBCXX_3.4.22 not found (required by clang) clang: /lib64/libstdc++.so.6: version GLIBCXX_3.4.20 not found (required by clang)
clang: /lib64/libstdc++.so.6: version GLIBCXX_3.4.21 not found (required by clang) clang: /lib64/libstdc++.so.6: version CXXABI_1.3.9 not found (required by clang)
llvm-config: /lib64/libstdc++.so.6: version CXXABI_1.3.9 not found (required by llvm-config) llvm-config: /lib64/libstdc++.so.6: version GLIBCXX_3.4.21 not found (required by llvm-config)

解决方案：声明新GCC相关的环境变量使动态链接器可以加载到新GCC的 libstdc++库

# 声明新GCC相关的环境变量，注意此步必须执行，否则后续GCC编译无法调用7.5版本新的运行库
cat << 'EOF' >> ~/.bashrc
export PATH=/usr/local/bin:$PATH
export LD_LIBRARY_PATH=/usr/local/lib64:$LD_LIBRARY_PATH
export LIBRARY_PATH=/usr/local/lib64:$LIBRARY_PATH
export C_INCLUDE_PATH=/usr/local/include
export CPLUS_INCLUDE_PATH=/usr/local/include/c++/7.5.0
EOF
source ~/.bashrc