How to set golang function as callback function of .net aot

Question content

I have a project at work, the main program is written in Golang, and there is a shared library written in C# .Net AOT .

The project requires calling functions between Golang code and C# .Net AOT.

The specific content is to pass a Golang function as a callback function to C# and call it in C#. But when I tested it, I found that the feature didn't work properly.

This is my test code:

In C#:

using System.Runtime.InteropServices;

namespace CSharp_Go
{
    public unsafe class Export
    {
        private static delegate* unmanaged[Stdcall]<int, int, int> _addDel;
        [UnmanagedCallersOnly(EntryPoint = "SetAddFunc")]
        public static void SetAddFunc(delegate* unmanaged[Stdcall]<int, int, int> addDel)
        {
            _addDel = addDel;
        }

        private static delegate* unmanaged<int> _testFun;
        [UnmanagedCallersOnly(EntryPoint = "SetTestFunc")]
        public static void SetTestFunc(delegate* unmanaged<int> testFun)
        {
            _testFun = testFun;
        }

        [UnmanagedCallersOnly(EntryPoint = "Test")]
        public static int Test()
        {
            int res = _testFun();
            Console.WriteLine($"in c# Test res:{res}");
            return res;
        }
        
        [UnmanagedCallersOnly(EntryPoint = "Add")]
        public static int Add(int a, int b)
        {
            Console.WriteLine($"in c# Add a:{a}, b:{b}");
            int res = 0;
            if (null != _addDel)
            {
                res = _addDel(a, b);
                Console.WriteLine($"in c# Add res:{res}, a:{a}, b:{b}");
            }
            
            return res;
        }
    }
}

Compilation command: dotnet publish -p:NativeLib=share -r win-x64 -c debug

Go code:

package main

import (
    "C"
    "fmt"
    "reflect"
    "syscall"
    "unsafe"
)

func Sum(a, b int32) int32 {
    //fmt.Printf("a：%d, b:%d\n", a, b)
    res := a + b
    return res
}

func main() {
    f := Sum
    ptrValue := reflect.ValueOf(f)
    ptr := unsafe.Pointer(ptrValue.Pointer())
    addr := uintptr(ptr)
    fmt.Printf("Func Addr: %v\n", addr)

    var input string
    fmt.Scanln(&input)
    fmt.Println(input)

    var aValue int32 = int32(1)
    var bValue int32 = int32(2)
    var a uintptr = uintptr(aValue)
    var b uintptr = uintptr(bValue)

    ptrVa := &aValue
    ptrA := &a
    fmt.Printf("va：%v, a: %v\n", ptrVa, ptrA)
    t := func() int32 {
        //fmt.Println(aValue, bValue)
        //pa := (*int32)(unsafe.Pointer(uintptr(aValue)))
        //a := *pa
        return aValue + bValue
    }
    ptrT := uintptr(unsafe.Pointer(reflect.ValueOf(t).Pointer()))
    fmt.Printf("Func Addr: %v\n", ptrT)

    fmt.Println("Hello go c#")
    maindll := syscall.NewLazyDLL("CSharp_Go.dll")

    setTestFunc := maindll.NewProc("SetTestFunc")
    test := maindll.NewProc("Test")

    //cb := syscall.NewCallback(t)
    r1, r2, err := setTestFunc.Call(ptrT)
    fmt.Println(r1, r2, err)

    r1, r2, err = test.Call()
    fmt.Println(r1, r2, err)

    setAddFunc := maindll.NewProc("SetAddFunc")
    add := maindll.NewProc("Add")

    r1, r2, err = setAddFunc.Call(addr)
    fmt.Println(r1, r2, err)

    r1, r2, err = add.Call(a, b)

    fmt.Println(r1, r2, err)
    fmt.Scanln(&input)
    fmt.Println(input)
}

I implemented a simple Add(int a, int b) function for testing. The input parameters are 1 and 2, the result should be 3, but it is not. When I was debugging, I found that the parameter list of the callback function was not 1 and 2, but some strange numbers. I tried both calling conventions, Stdcall and Cdecl, but they couldn't solve the problem.

What is the reason for this and how to solve it?

debug

This is the complete output log

<code>
Func Addr: 15405888
6
6
va：0xc00000e128, a: 0xc00000e130
Func Addr: 15410016
Hello go c#
2259596893072 2260255909544 The operation completed successfully.
in c# Test res:12144
12144 0 The operation completed successfully.
2259596893072 15405888 The operation completed successfully.
in c# Add a:1, b:2
in c# Add res:31533024, a:1, b:2
31533024 0 The operation completed successfully.
</code>

Correct answer

You need to use cgo to export go functions

package main

/*
extern int sum(int, int);
//static inline void CallMyFunction(int a, int b) {
//    sum(a, b);
//}
*/
import "C"
import (
    "fmt"
    "reflect"
    "syscall"
    "unsafe"
)

//export sum
func sum(a, b C.int) C.int {
    res := a + b
    fmt.Println(a, "+", b , "=", res )
    return res
}

func main() {
    fmt.Println("Hello go c#")
    var input string
    fmt.Scanln(&input)
    fmt.Println(input)

    //C.CallMyFunction(3, 4)

    var aValue int32 = int32(3)
    var bValue int32 = int32(4)
    var a uintptr = uintptr(aValue)
    var b uintptr = uintptr(bValue)

    f := C.sum
    ptrValue := reflect.ValueOf(f)
    ptr := unsafe.Pointer(ptrValue.Pointer())
    addr := uintptr(ptr)
    fmt.Printf("Func Addr: %v\n", addr)

    maindll := syscall.NewLazyDLL("CSharp_Go.dll")
    //maindll := syscall.NewLazyDLL("Cpp_Go.dll")
    setAddFunc := maindll.NewProc("SetAddFunc")
    add := maindll.NewProc("Add")

    r1, r2, err := setAddFunc.Call(addr)
    fmt.Println(r1, r2, err)

    r1, r2, err = add.Call(a, b)
    fmt.Println(r1, r2, err)

    fmt.Scanln(&input)
    fmt.Println(input)
}

The output is:

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