前言
现在看的资料都是编译 openjdk7 的，openjdk8好像已经 openjdk7 编译方式大一样，按照前辈的文章使用
make sanity
会提示找不到 sanity 规则，然后编译过程其实基本就直接
./configuremake all
官方的 README 写的很清楚。
下面记录下过程
下载代码hg clone jdk8ucd jdk8u bash ./get_source.sh
然后下载代码，进入代码目录：
cd jdk8u
代码目录中有一个README-builds.html描述了如何 build 整个系统,一些细节需要自己去寻找。
安装依赖sudo aptitude build-dep openjdk-7 sudo aptitude install openjdk-7-jdk配置环境变量export LANG=C export PATH="/usr/lib/jvm/java-7-openjdk/bin:${PATH}"配置编译选项bash ./configure
这样生成相应默认配置，如果有需要，比如想编译出调试版本的，可以给configure加参数。
A new configuration has been successfully created in/home/minix/SourceCode/openjdk8/jdk8u/build/linux-x86-normal-server-releaseusing default settings.Configuration summary:* Debug level: release* JDK variant: normal* JVM variants: server* OpenJDK target: OS: linux, CPU architecture: x86, address length: 32Tools summary:* Boot JDK:java version "1.7.0_17" Java(TM) SE Runtime Environment (build 1.7.0_17-b02) Java HotSpot(TM) Server VM (build 23.7-b01, mixed mode) (at /home/minix/Software/jdk1.7.0_17)* C Compiler:gcc-4.6 (Ubuntu/Linaro 4.6.3-1ubuntu5) version 4.6.3 (at /usr/bin/gcc-4.6)* C++ Compiler: g++-4.6 (Ubuntu/Linaro 4.6.3-1ubuntu5) version 4.6.3 (at /usr/bin/g++-4.6)Build performance summary:* Cores to use: 3* Memory limit: 3878 MB* ccache status: not installed (consider installing)Build performance tip: ccache gives a tremendous speedup for C++ recompilations.You do not have ccache installed. Try installing it.You might be able to fix this by running ‘sudo apt-get install ccache’.
可以看出提示缺少 ccache 包，按提示安装就可以了。从提示可以看出，编译级别是release，另外还有几种编译级别，可以在调试时候提供更多的信息。例如：
bash ./configure –enable-debug
这样会生成fastdebug版本的配置信息：
A new configuration has been successfully created in/home/minix/openjdk8/jdk8u/build/linux-x86-normal-server-fastdebugusing configure arguments ‘–enable-debug’.Configuration summary:* Debug level: fastdebug* JDK variant: normal* JVM variants: server* OpenJDK target: OS: linux, CPU architecture: x86, address length: 32Tools summary:* Boot JDK:java version "1.7.0_17" Java(TM) SE Runtime Environment (build 1.7.0_17-b02) Java HotSpot(TM) Server VM (build 23.7-b01, mixed mode) (at /home/minix/Software/jdk1.7.0_17)* C Compiler:gcc-4.6 (Ubuntu/Linaro 4.6.3-1ubuntu5) version 4.6.3 (at /usr/bin/gcc-4.6)* C++ Compiler: g++-4.6 (Ubuntu/Linaro 4.6.3-1ubuntu5) version 4.6.3 (at /usr/bin/g++-4.6)Build performance summary:* Cores to use: 3* Memory limit: 3878 MB* ccache status: installed and in use
注意编译的级别已经变成fastdebug了。
–enable-debug其实相当于 –with-debug-level=fastdebug, 可以通过这样的参数选项指定编译级别。一共可以指定三种级别:release, fastdebug, slowdebug,slowdebug含有最丰富的调试信息，没有这些信息，很多执行可能被优化掉，我们单步执行时，可能看不到一些变量的值。所以最好指定slowdebug为编译级别
编译
编译直接
make
就可以了，如果提示
No CONF given, but more than one configuration found in /home/minix/openjdk8/jdk8u//build.Available configurations:* linux-x86-normal-server-fastdebug* linux-x86-normal-server-releasePlease retry building with CONF=<config pattern> (or SPEC=<specfile>)
需要指定使用哪个编译配置：
make CONF=linux-x86-normal-server-fastdebug
最后编译成功后，会提示：
—– Build times ——-Start 2014-08-22 10:56:52End 2014-08-22 11:16:3100:00:30 corba00:13:38 hotspot00:00:22 jaxp00:00:30 jaxws00:04:10 jdk00:00:29 langtools00:19:39 TOTAL
查看build目录，可以看到linux-x86-normal-server-fastdebug
切换到jdk/bin目录：
cd linux-x86-normal-server-fastdebug/jdk/bin/
运行可执行文件 java
./java -version
会得到提示
openjdk version "1.8.0-internal-fastdebug"OpenJDK Runtime Environment (build 1.8.0-internal-fastdebug-minix_2014_08_22_10_56-b00)OpenJDK Server VM (build 25.40-b05-fastdebug, mixed mode)调试
下面展示一个启动GDB, 加断点，并运行一个 Java 程序的过程。
$ gdb javaGNU gdb (Ubuntu/Linaro 7.4-2012.04-0ubuntu2.1) 7.4-2012.04Copyright (C) 2012 Free Software Foundation, Inc.License GPLv3+: GNU GPL version 3 or later <>This is free software: you are free to change and redistribute it.There is NO WARRANTY, to the extent permitted by law. Type "show copying"and "show warranty" for details.This GDB was configured as "i686-linux-gnu".For bug reporting instructions, please see:<>…Reading symbols from /home/minix/openjdk8/jdk8u/build/fastdebug/jdk/bin/java…done.(gdb) b mainBreakpoint 1 at 0x8048410: file /home/minix/openjdk8/jdk8u/jdk/src/share/bin/main.c, line 94.(gdb) r -classpath PossibleReorderingStarting program: /home/minix/openjdk8/jdk8u/build/fastdebug/jdk/bin/java -classpath PossibleReordering[Thread debugging using libthread_db enabled]Using host libthread_db library "/lib/i386-linux-gnu/libthread_db.so.1".Breakpoint 1, main (argc=3, argv=0xbfffeca4)at /home/minix/openjdk8/jdk8u/jdk/src/share/bin/main.c:94
，真正的寂寞是在人群中，当你面对许多熟悉的脸，
