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
./configure
make all
官方的 README 写的很清楚。
下面记录下过程
下载代码
hg clone http://hg.openjdk.java.net/jdk8u/jdk8u jdk8u
cd 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-release
using default settings.
Configuration summary:
* Debug level: release
* JDK variant: normal
* JVM variants: server
* OpenJDK target: OS: linux, CPU architecture: x86, address length: 32
Tools 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-fastdebug
using configure arguments '--enable-debug'.
Configuration summary:
* Debug level: fastdebug
* JDK variant: normal
* JVM variants: server
* OpenJDK target: OS: linux, CPU architecture: x86, address length: 32
Tools 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-release
Please retry building with CONF= (or SPEC=)
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 10:56:52
End 2014-08-22 11:16:31
00:00:30 corba
00:13:38 hotspot
00:00:22 jaxp
00:00:30 jaxws
00:04:10 jdk
00:00:29 langtools
00:19:39 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 java
GNU gdb (Ubuntu/Linaro 7.4-2012.04-0ubuntu2.1) 7.4-2012.04
Copyright (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: