Call mono-2.0-sgen.dll with syscall got "not a valid Win32 application"

Question

I want to execute HelloWorldConsole.exe with an shipped Mono Framework through Go.

So I want to call mono-2.0-sgen.dll funtion "mono_main" to execute the exe. mono-2.0-sgen.dll is a PE32 executable for MS Windows, see .

But I get the error "not a valid Win32 application"

_ = os.Setenv("MONO_PATH", `\mono\lib\mono\4.5;C:\DEV\HelloWorldConsole\HelloWorldConsole\bin\Debug`)
_ = os.Setenv("MONO_CFG_DIR", `"C:\Program Files (x86)\Mono\etc"`)
_ = os.Setenv("MONO_CONFIG", `"C:\Program Files (x86)\Mono\etc\mono\config"`)

mono := `C:\Program Files (x86)\Mono\bin\mono-2.0-sgen.dll`
app := `C:\DEV\HelloWorldConsole\HelloWorldConsole\bin\Debug\HelloWorldConsole.exe`

fmt.Println("Execute")

var mod = syscall.NewLazyDLL(mono)
var proc = mod.NewProc("mono_main")

ret, _, _ := proc.Call(0,
    uintptr(unsafe.Pointer(syscall.StringToUTF16Ptr("mono.exe"))),
    uintptr(unsafe.Pointer(syscall.StringToUTF16Ptr(app)))  )

Same behavior with windows.NewLazySystemDLL

dll := windows.NewLazySystemDLL(mono)
lazyProc := dll.NewProc("mono_main")
lazyProc.Call()

Function Name

Full Error:

panic: Failed to load C:\Program Files (x86)\Mono\bin\mono-2.0-sgen.dll: %1 is **not a valid Win32 application**.

Answer 1

%1 is not a valid Win32 application

The error %1 is not a valid Win32 application is a discription of Win32 error code from windows itself.

The Win32 error code itself is 0x000000C1 ERROR_BAD_EXE_FORMAT , see docs.microsoft.com .

BAD_EXE_FORMAT means you call a x86 dll within a x64 process. You must use the x86 variant of Go, eg go1.12.1.windows-386.zip from https://golang.org/dl/ .

Now must change the GOROOT and PATH to the extracted bin folder and then you are ready to go.

Type of Arguments

When you call mono_main you need to consume the this function in the right way. If you take an look at the implementation you see that the signature is int mono_main (int argc, char* argv[]); . argc and argv is a widly used pattern, see here .

Working Sample

func main() {
    _ = os.Setenv("MONO_PATH", `C:\DEV\HelloWorldConsole\HelloWorldConsole\bin\x86\Debug\mono\lib\mono\4.5;C:\DEV\HelloWorldConsole\HelloWorldConsole\bin\x86\Debug\`)
    _ = os.Setenv("MONO_CFG_DIR", `C:\DEV\HelloWorhpm.goldConsole\HelloWorldConsole\bin\x86\Debug\mono\etc`)
    _ = os.Setenv("MONO_CONFIG", `C:\DEV\HelloWorldConsole\HelloWorldConsole\bin\x86\Debug\mono\etc\mono\config`)

    _ = os.Chdir(`C:\DEV\HelloWorldConsole\HelloWorldConsole\bin\x86\Debug\`)

    mono := `C:\DEV\HelloWorldConsole\HelloWorldConsole\bin\x86\Debug\mono\bin\mono-2.0-sgen.dll`

    // https://github.com/mono/mono/blob/c5b88ec4f323f2bdb7c7d0a595ece28dae66579c/mcs/tools/mkbundle/template_main.c#L1
    dll := windows.NewLazySystemDLL(mono)
    lazyProc := dll.NewProc("mono_main")

    dotNetAssembly := []byte(`HelloWorldConsole.exe`)

    var argumentData [260]byte
    ptr := unsafe.Pointer(&argumentData)

    copy(argumentData[:], dotNetAssembly)

    args := [2]uintptr{0, uintptr(ptr)}

    _, _, _ = lazyProc.Call(2, uintptr(unsafe.Pointer(&args)))
}