在 Go 程序中使用 cgo 共享库

Question

试图测试cgo ，所以我写了以下内容：

//go:build lib
// +build lib

package main

import "C"
import "fmt"

//export HelloWorld
func HelloWorld() {
    fmt.Printf("hello world")
}

func main() {}

// go build -tags lib -buildmode=c-shared -o golib.a lib.go

并将其编译为：

$ go build -tags lib -buildmode=c-shared -o golib.a lib.go

尝试在另一个代码中使用生成的共享库：

//go:build app
// +build app

package main

// #cgo CFLAGS: -g -Wall
// #include <stdlib.h>
// #include "golib.h"
import "C"

func main() {
    C.HelloWorld()
}

// go run main.go

但我收到以下错误：

# command-line-arguments
Undefined symbols for architecture x86_64:
  "_HelloWorld", referenced from:
      __cgo_a844f0d618a1_Cfunc_HelloWorld in _x002.o
     (maybe you meant: __cgo_a844f0d618a1_Cfunc_HelloWorld)
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
# command-line-arguments
cgo-gcc-prolog:47:33: warning: unused variable '_cgo_a' [-Wunused-variable]

此外，我在 mac 上使用 VS 代码收到以下错误：

go list failed to return CompiledGoFiles. This may indicate failure to perform cgo processing; try building at the command line. See https://golang.org/issue/38990

Answer 1

您不能在 Go 程序中使用 cgo 共享库，因为在同一进程中不能有多个 Go 运行时。

尝试这样做会给出错误：

# command-line-arguments
cgo-gcc-prolog:67:33: warning: unused variable '_cgo_a' [-Wunused-variable]
fatal error: unexpected signal during runtime execution
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x43fd5e2]

goroutine 1 [running, locked to thread]:
runtime.throw({0x40a875b?, 0x1c00011b800?})
        /usr/local/go/src/runtime/panic.go:992 +0x71 fp=0x1c00004a960 sp=0x1c00004a930 pc=0x402f6d1
runtime: unexpected return pc for runtime.sigpanic called from 0x43fd5e2
stack: frame={sp:0x1c00004a960, fp:0x1c00004a9b0} stack=[0x1c00004a000,0x1c00004b000)
....
0x000001c00004aaa0:  0x0000000000000000  0x0000000000000000 
runtime.sigpanic()
        /usr/local/go/src/runtime/signal_unix.go:781 +0x3a9 fp=0x1c00004a9b0 sp=0x1c00004a960 pc=0x4043449
exit status 2

要从 go 调用 c 代码，有 3 种可能的方法：

1. 内联编码，如：

package main

//#include  <stdio.h>
//int Add(int a, int b){
//    printf("Welcome from external C function\n");
//    return a + b;
//}
import "C"
import "fmt"

func main() {
    fmt.Println(C.Add(5, 2))
}

2. Static 链接，您同时拥有.c和.h文件，如：

// lib.c
#include  <stdio.h>
int Add(int a, int b){
    printf("Welcome from external C function\n");
    return a + b;
}

和

// libadd.h
int Add(int, int);

go 文件为：

// main.go
package main

// #include "libadd.h"
import "C"
import "fmt"

func main() {
    x := C.Add(1, 2)
    fmt.Println(x)

}

我们必须将文件运行为go run. or go run github.io/xxx // go run main.go will not work as it will consider main.go only, and not consider the C file

3. Dynamic linking, where you compile the above c file as clang -shared -fpic -Wall -g lib.c -o libadd.so and have the go file as:

// main.go
package main

//#cgo CFLAGS: -g -Wall
//#cgo LDFLAGS: -L. -ladd
//#include "libadd.h"
import "C"
import "fmt"

func main() {
    x := C.Add(1, 2)
    fmt.Println(x)
}

这里可以使用go run main.go因为库是通过硬代码连接的，为了分发二进制文件，共享库loadadd.so需要与相同的二进制文件分发并存在于同一文件夹中。

我为每个案例上传了单独的文件夹 [这里][1]

奖金要使用 c 程序调用 go 中生成的共享库，我们可以使用以下代码：

// main.c
#include <stdio.h>
#include "libadd.h" // calling C file
#include "libgo.h" // calling shared library generated by GO

int main()
{
    HelloWorld();
    int x = Add(1, 2);
    printf("%d",x);
    return 0;
}

将文件编译为：``bash clang -o main -L。 -ladd -lgo main.c // -ladd => -l（库）是 libadd

  [1]: https://github.com/hajsf/tutorial/tree/master/ffi