关于configure的build,host,target编译选项的理解.

参考资料:

1. http://en.wikipedia.org/wiki/Cross_compile
2. http://www.airs.com/ian/configure/configure_5.html#SEC30
3. http://oss.lzu.edu.cn/blog/blog.php?/do_showone/tid_116.html

1. build 就是你现在使用的机器。
2. host 就是你编译好的程序能够运行的平台。
3. target 编译程序能够处理的平台。一般都用在构建编译本身的时候(gcc), 才用target, 也就是说平时我们所说的交叉编译用不到target.

    The GNU autotools packages (i.e. autoconf, automake, and libtool) use the notion of a build platform, a host platform, and a target platform.
    The build platform is where the code is actually compiled.
    The host platform is where the compiled code will execute.
    The target platform usually only applies to compilers. It represents what type of object code the package itself will produce (such as cross-compiling a cross-compiler); otherwise the target platform setting is irrelevant. For example, consider cross-compiling a video game that will run on a Dreamcast. The machine where the game is compiled is the build platform while the Dreamcast is the host platform.
   

    When building cross compilation tools, there are two different systems involved: the system on which the tools will run, and the system for which the tools generate code.
    The system on which the tools will run is called the host system.
    The system for which the tools generate code is called the target system.
    For example, suppose you have a compiler which runs on a GNU/Linux system and generates ELF programs for a MIPS embedded system. In this case the GNU/Linux system is the host, and the MIPS ELF system is the target. Such a compiler could be called a GNU/Linux cross MIPS ELF compiler, or, equivalently, a ‘i386-linux-gnu’ cross ‘mips-elf’ compiler.

Target usually have a meaning for developemt tool only.
    比如: 在386的平台上编译可以运行在arm板的程序 ./configure –build=i386-linux,–host=arm-linux就可以了.
    因为一般我们都是编译程序而不是编译工具.
    如果我们编译工具,比如gcc,这个target就有用了.如果我们需要在一个我们的机器上为arm开发板编译一个可以处理 mips程序的gcc,那么target就是mips了.

Example:
    1. ./configure --build=mipsel-linux --host=mipsel-linux
--target=mipsel-linux' will build native mipsel-linux binutils on
mipsel-linux.
    2. ./configure --build=i386-linux --host=mipsel-linux
--target=mipsel-linux' will cross-build native mipsel-linux binutils on
i386-linux.
    3. ./configure --build=i386-linux --host=i386-linux
--target=mipsel-linux' will build mipsel-linux cross-binutils on
i386-linux.
    4. ./configure --build=mipsel-linux --host=i386-linux
--target=mipsel-linux' will cross-build mipsel-linux cross-binutils for
i386-linux on mipsel-linux.

    As you see, only if $build != $host a cross-compilation is performed.