Go Fails to Find Procedure in DLL

Why Go fails to find the specified procedure in dll?

I have a my.dll library compiled for Windows x86 (The OS is Windows 7 x64; but I am using Go x86 binary - with LiteIDE - and the C# code is also explicitly compiled for x86 architecture). And I use it from C# and it works:

[DllImport("my.dll", EntryPoint = "my_function")]
public static extern double my_function(double x);

But when I try to use it (here I am trying just to find it) from Go by:

var (
	dllMine     = syscall.NewLazyDLL("my.dll")
	my_function = dllMine.NewProc("my_function")
)

func main() {
	err := my_function.Find()
	if err != nil {
		fmt.Println(err)
		return
	}
    //...
}

It says Failed to find my_function procedure in my.dll: The specified procedure could not be found.. The my.dll file resides at the same directory with the generated .exe file. The entry point name ("my_function") does exists because it's working fine when is imported in C# and it does not say Failed to load my.dll: The specified module could not be found..

Actual pieces: The library I am trying to call is swedll32.dll which is the core library of Swiss Ephemeris (can be downloaded here - GNU) and just for testing this scenario the function to be called is swe_julday; for reproducing the error, with this signature:

double swe_julday(
    int year, int month, int day, double hour,
    int gregflag);     /* Gregorian calendar: 1, Julian calendar: 0 */

Another thing is my GOROOT environment parameter is actually a NTFS junction point (so I can switch between x86 and x64 versions) - but I do not think it's relevant, because the output .exe app is being generated without any problem (just for the sake of confessing all my sins!).

I have downloaded your dll from http://www.astro.com/ftp/swisseph/sweph.zip to see if swe_julday function is in there:

C:\foo>dumpbin /exports swedll32.dll | find "swe_julday"
         74   49 0000C440 _swe_julday@24
         75   4A 0000D4A0 _swe_julday_d@24

And I don't see swe_julday function in there. Instead I see _swe_julday@24 function. So if I change your program to:

C:\foo>type foo.go
package main

import (
        "syscall"
        "fmt"
)

var (
        dllMine     = syscall.NewLazyDLL("swedll32.dll")
        my_function = dllMine.NewProc("_swe_julday@24")
)

func main() {
        err := my_function.Find()
        if err != nil {
                fmt.Println(err)
                return
        }
        //...
}

it runs without any errors:

C:\foo>go run foo.go

C:\foo>