我们知道，关于 GCC 在 CentOS 下通过 yum 安装默认版本号，CentOS 5 是 4.1.2；CentOS 6 是 4.4.7；CentOS 7 是 4.8.3。很多时候在编译安装软件都需要高版本的 GCC，否则就会报错。那么如何升级 GCC 的版本呢？
首先要确认升级到的 GCC 版本号。目前 GCC 的最新版已经到了 5.2，而 CentOS 7 则依然使用其 4.8，所以基于兼容性考虑，可以选择升级到 4.8.5。GCC 官网：https://gcc.gnu.org。
需要注意，编译安装 GCC 内存不小于 1GB，Swap 不小于 1GB，硬盘最低不小于 10GB，否则极有可能会中途报错退出。编译安装完后，目录 gcc-4.8.5 将会有 5GB 之多。
1. 下载源码
$ wget ftp://ftp.gnu.org/gnu/gcc/gcc-4.8.5/gcc-4.8.5.tar.gz
2. 下载依赖包
编译安装 GCC 需要依赖 mpc，mpfr，gmp，isl 包。前四个包是 GNU 软件，使用 GCC 源码里自带脚本可以轻松下载；最后一个 isl 不是 GNU 项目，需要我们手动去下载。
$ tar zxf gcc-4.8.5.tar.gz
$ cd gcc-4.8.5
$ ./contrib/download_prerequisites
--2019-06-06 16:18:09-- ftp://gcc.gnu.org/pub/gcc/infrastructure/mpfr-2.4.2.tar.bz2
=> “mpfr-2.4.2.tar.bz2”
Resolving gcc.gnu.org... 209.132.180.131
Connecting to gcc.gnu.org|209.132.180.131|:21... connected.
Logging in as anonymous ... Logged in!
==> SYST ... done. ==> PWD ... done.
==> TYPE I ... done. ==> CWD (1) /pub/gcc/infrastructure ... done.
==> SIZE mpfr-2.4.2.tar.bz2 ... 1077886
==> PASV ... done. ==> RETR mpfr-2.4.2.tar.bz2 ... done.
Length: 1077886 (1.0M) (unauthoritative)
100%[=================================================================================>] 1,077,886 249K/s in 4.2s
2019-06-06 16:18:19 (249 KB/s) - “mpfr-2.4.2.tar.bz2” saved [1077886]
--2019-06-06 16:18:20-- ftp://gcc.gnu.org/pub/gcc/infrastructure/gmp-4.3.2.tar.bz2
=> “gmp-4.3.2.tar.bz2”
Resolving gcc.gnu.org... 209.132.180.131
Connecting to gcc.gnu.org|209.132.180.131|:21... connected.
Logging in as anonymous ... Logged in!
==> SYST ... done. ==> PWD ... done.
==> TYPE I ... done. ==> CWD (1) /pub/gcc/infrastructure ... done.
==> SIZE gmp-4.3.2.tar.bz2 ... 1897483
==> PASV ... done. ==> RETR gmp-4.3.2.tar.bz2 ... done.
Length: 1897483 (1.8M) (unauthoritative)
100%[=================================================================================>] 1,897,483 210K/s in 7.7s
2019-06-06 16:18:30 (239 KB/s) - “gmp-4.3.2.tar.bz2” saved [1897483]
--2019-06-06 16:18:31-- ftp://gcc.gnu.org/pub/gcc/infrastructure/mpc-0.8.1.tar.gz
=> “mpc-0.8.1.tar.gz”
Resolving gcc.gnu.org... 209.132.180.131
Connecting to gcc.gnu.org|209.132.180.131|:21... connected.
Logging in as anonymous ... Logged in!
==> SYST ... done. ==> PWD ... done.
==> TYPE I ... done. ==> CWD (1) /pub/gcc/infrastructure ... done.
==> SIZE mpc-0.8.1.tar.gz ... 544950
==> PASV ... done. ==> RETR mpc-0.8.1.tar.gz ... done.
Length: 544950 (532K) (unauthoritative)
100%[=================================================================================>] 544,950 286K/s in 1.9s
2019-06-06 16:18:35 (286 KB/s) - “mpc-0.8.1.tar.gz” saved [544950]
$ wget http://isl.gforge.inria.fr/isl-0.14.tar.gz
$ tar zvxf isl-0.14.tar.gz
$ ln -s lsl isl-0.14
在此脚本里可以看到依赖包的版本号依次是 mpc-0.8.1，mpfr-2.4.2，gmp-4.3.2；另外我们下载 isl-0.14。
3. 编译安装
为了避免在编译过程中，受原来系统自定义的一堆环境影响，建议先 unset 这些环境设置：
$ unset LIBRARY_PATH CPATH C_INCLUDE_PATH PKG_CONFIG_PATH CPLUS_INCLUDE_PATH INCLUDE
完整编译安装步骤如下：
$ mkdir gcc-build-4.8.5
$ cd gcc-build-4.8.5
$ unset LIBRARY_PATH CPATH C_INCLUDE_PATH PKG_CONFIG_PATH CPLUS_INCLUDE_PATH INCLUDE
$ ../configure -enable-checking=release -enable-languages=c,c++ -disable-multilib --prefix=/Bioinfo/SoftWare/gcc-4.8.5
$ make
$ make install
.....
----------------------------------------------------------------------
Libraries have been installed in:
/Bioinfo/SoftWare/gcc-4.8.5/lib/../lib64
If you ever happen to want to link against installed libraries
in a given directory, LIBDIR, you must either use libtool, and
specify the full pathname of the library, or use the `-LLIBDIR'
flag during linking and do at least one of the following:
- add LIBDIR to the `LD_LIBRARY_PATH' environment variable
during execution
- add LIBDIR to the `LD_RUN_PATH' environment variable
during linking
- use the `-Wl,-rpath -Wl,LIBDIR' linker flag
- have your system administrator add LIBDIR to `/etc/ld.so.conf'
See any operating system documentation about shared libraries for
more information, such as the ld(1) and ld.so(8) manual pages.
----------------------------------------------------------------------
......
如果需要重新 configure 或在 make 中途出错需要退出，最好把当前目录下的所有东西都删除干净。可以执行下面指令清空 编译目录下的相关文件，包括 makefile：
$ make distclean
4. 配置环境变量
GCC 安装完成后，需要包新安装的 gcc 添加到 PATH 个人相应的 LD_LIBRARY_PATH ：
export PATH=/Bioinfo/SoftWare/gcc-4.8.5/bin:$PATH
export LD_LIBRARY_PATH=/Bioinfo/SoftWare/gcc-4.8.5/lib64:$LD_LIBRARY_PATH
如果不想把新装 GCC 添加到 ~/.bashrc 中的 PATH 和 LD_LIBRARY_PATH 让它永久起作用，但是在安装软件时又想使用新安装的高级版本的 GCC 来编译软件，可以在软件编译前先执行上面两个 export 语句再执行编译安装命令；或者在软件编译安装时直接在编译参数中添加 gcc/g++ 和其动态库的路径就可以。
5. 参考资料
- 秋水逸冰，《在CentOS下编译安装GCC》，WorldPress 博客
- 佚名，《How can I understand these dreadful errors when building gcc-4.8.2?》，StackOverflow
- ljpwinxp，《Centos 6.9 编译安装gcc 4.8.5》，51CTO
- 代码日志，《c – 构建gcc-4.8.2时如何理解这些可怕的错误？》, 博客
- Benjamin Berhault, 《Build and Install the Last GCC on RHEL/CentOS 7》，Ben's Jekyll Blog
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