Go中的交叉编译问题

 ~ $ go help environment
...
  GOARCH
    The architecture, or processor, for which to compile code.
    Examples are amd64, 386, arm, ppc64.
...
  GOOS
    The operating system for which to compile code.
    Examples are linux, darwin, windows, netbsd.
...
  CGO_ENABLED
    Whether the cgo command is supported. Either 0 or 1.

export CGO_ENABLED=0 GOOS=linux GOARCH=amd64 go build main.go
export CGO_ENABLED=0 GOOS=windows GOARCH=amd64 go build main.go

export CGO_ENABLED=0 GOOS=darwin GOARCH=amd64 go build main.go
export CGO_ENABLED=0 GOOS=windows GOARCH=amd64 go build main.go

SET CGO_ENABLED=0 GOOS=darwin GOARCH=amd64 go build main.go
SET CGO_ENABLED=0 GOOS=linux GOARCH=amd64 go build main.go

// +build

package main
​
// 引用了Go所能支持的所有架构体系库代码，根据GOARCH选择对应的体系代码
import (  
  "cmd/compile/internal/amd64"
  "cmd/compile/internal/arm"
  "cmd/compile/internal/arm64"
 ....
  "cmd/compile/internal/x86"
...
)
​
// 初始化代码
var archInits = map[string]func(*gc.Arch){
  "386":      x86.Init,
  "amd64":    amd64.Init,
  "arm":      arm.Init,
  "arm64":    arm64.Init,
...
}
​
func main() {
  // disable timestamps for reproducible output
  log.SetFlags(0)
  log.SetPrefix("compile: ")
​
// 通过objabi.GOARCH选择对应的架构体系
  archInit, ok := archInits[objabi.GOARCH]
...
  gc.Main(archInit)
...
}

var (
  defaultGOROOT string // set by linker
​
...
  GOROOT   = envOr("GOROOT", defaultGOROOT)
  GOARCH   = envOr("GOARCH", defaultGOARCH)
  GOOS     = envOr("GOOS", defaultGOOS)
...
)

// Code generated by go tool dist; DO NOT EDIT.
​
package objabi
​
import "runtime"
​
...
const defaultGOOS = runtime.GOOS
const defaultGOARCH = runtime.GOARCH
...

// GOARCH is the running program's architecture target:
// one of 386, amd64, arm, s390x, and so on.
const GOARCH string = sys.GOARCH

// Code generated by gengoos.go using 'go generate'. DO NOT EDIT.
​
// 我的机器平台是amd64，且未对GOARCH的值做修改。因此这里的构建标签是amd64.
// +build amd64
​
package sys
​
const GOARCH = `amd64`

package main
​
import "fmt"
​
func main() {
  fmt.Println("mike")
  speak("hello")
}

//+build speak
​
package main
​
func speak(s string) {
  println("speak:", s)
}

$ go build -o main
$ ./main

$ go build -tags speak -o main
$ ./main