老年人编译系列-go cmd/dist源码

dist是用来编译go语言的工具，而且dist本身是由go语言写的
所以可以用低版本的go编译dist, 再用dist编译高版本的go
/src/cmd/dist是go dist工具的代码目录
main.go中的main为入口函数
主要的流程为

• 检测操作系统
• 检测系统架构
• bginit() //启动一组后端运行的goroutine， 用于在后台运行go
• xinit() //初始化全局变量/状态
• xmain() //执行全局commands变量中存储的操作
• xexit() //资源检查/进程退出
  查看usage()函数可知

func usage() {
    xprintf(`usage: go tool dist [command]
Commands are:
banner         print installation banner
bootstrap      rebuild everything
clean          deletes all built files
env [-p]       print environment (-p: include $PATH)
install [dir]  install individual directory
list [-json]   list all supported platforms
test [-h]      run Go test(s)
version        print Go version

All commands take -v flags to emit extra information.
`)
    xexit(2)
}

查看commands的定义

// commands records the available commands.
var commands = map[string]func(){
    "banner":    cmdbanner,
    "bootstrap": cmdbootstrap,
    "clean":     cmdclean,
    "env":       cmdenv,
    "install":   cmdinstall,
    "list":      cmdlist,
    "test":      cmdtest,
    "version":   cmdversion,
}

着重看cmdbootstrap流程
cmdbootstrap流程中

• 检查rebuildall, debug, nobanner三个参数
• setup()
• checkCC()
• bootstrapBuildTools()
• install("runtime")
• install("cmd/go")
• goInstall(goBootstrap, append([]string{"-i"}, toolchain...)...)
• goInstall(goBootstrap, append([]string{"-a", "-i"}, toolchain...)...)
• goInstall(goBootstrap, targets...)