How to use linkname in go language

In the source code of the go language, you will find many things. The code only has function signatures, but cannot see the function body, such as:

// src/os/ 68 linesfunc runtime_beforeExit() // implemented in runtime

Here we only see the function signature, but we can't see the function body. We searched the globally and found that its function body is definedsrc/runtime/middle

// os_beforeExit is called from (0).
//go:linkname os_beforeExit os.runtime_beforeExit
func os_beforeExit() {
  if raceenabled {
    racefini()
  }
}

It connects the function signature and the function body through go:linkname. So, can we implement this in the code? Since it can be used in library functions, can we also use it in our own code structure? The following experiments will implement this usage step by step

Create a project directory

$mkdir demo && cd demo

go mod initialize project directory

$go mod init demo

Create function signature pkg and function body pkg

$mkdir hello
$mkdir link

Writing test code

$cd hello
// Function signature$vim 
package hello
import (
  _ "demo/link"
)
func Hello()
// Function body$vim 
package link
import _ "unsafe"
//go:linkname helloWorld demo/
func helloWorld() {
  println("hello world!")
}

Execute code

$cd demo
vim 
package main
import (
  "demo/hello"
)
func main() {
  ()
}

Compile and run

go run 
# demo/hello
hello/:7:6: missing function body

The assembly file label added in the hello folder can be executed through compilation

$cd hello && touch 
$go run 
hello world!

Summarize

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