I have a dynamic library from which I need to call a procedure in my Go program, but I can't seem to get it right. I have another program written in C# which uses this DLL and according to dnSpy dllimport compiles to:
[DllImport("Library.dll", CharSet = CharSet.Ansi, ExactSpelling = true, SetLastError = true)]
public static extern void Calc(double[] Input, [MarshalAs(UnmanagedType.VBByRefStr)] ref string Pattern, [MarshalAs(UnmanagedType.VBByRefStr)] ref string Database_path, double[] Output);
So basing on this I tried to call it in my code like so:
func main() {
lib := syscall.NewLazyDLL("Library.dll")
proc := lib.NewProc("Calc")
input := [28]float64{0.741, 0.585, 2, 12, 1, 1, 1, 101325, 2500, 3, 20, 17.73, 17.11, 45, 1, 0, 80, 60, 0, 0, 0, 0, 0, 0, 0, 20, 0, 0}
output := [20]float64{}
tubePattern := marshalAnsi("P8-16G-E145/028")
basePath, _ := filepath.Abs(".")
databasePath := marshalAnsi(basePath)
a1 := uintptr(unsafe.Pointer(&input))
a2 := uintptr(unsafe.Pointer(tubePattern))
a3 := uintptr(unsafe.Pointer(databasePath))
a4 := uintptr(unsafe.Pointer(&output))
ret, _, _ := proc.Call(a1, a2, a3, a4)
log.Println(ret)
log.Println(output)
}
func marshalAnsi(input string) *[]byte {
var b bytes.Buffer
writer := transform.NewWriter(&b, charmap.Windows1252.NewEncoder())
writer.Write([]byte(input))
writer.Close()
output := b.Bytes()
return &output
}
This results in unhandled delphi exception:
Exception 0xeedfade 0x31392774 0x32db04e4 0x7677ddc2
PC=0x7677ddc2
syscall.Syscall6(0x314af7d0, 0x4, 0x10ee7eb8, 0x10ed21a0, 0x10ed21d0, 0x10ee7d78, 0x0, 0x0, 0x0, 0x0, ...)
C:/Go32/src/runtime/syscall_windows.go:184 +0xcf
syscall.(*Proc).Call(0x10ed21e0, 0x10ed85e0, 0x4, 0x4, 0x10, 0x49bee0, 0x533801, 0x10ed85e0)
C:/Go32/src/syscall/dll_windows.go:152 +0x32e
syscall.(*LazyProc).Call(0x10ecb9c0, 0x10ed85e0, 0x4, 0x4, 0x0, 0x0, 0x4c6d70, 0x5491a0)
C:/Go32/src/syscall/dll_windows.go:302 +0x48
main.main()
C:/Users/Krzysztof Kowalczyk/go/src/danpoltherm.pl/dllloader/main.go:32 +0x2c0
eax 0x19f3f0
ebx 0x31392774
ecx 0x7
edx 0x0
edi 0x10ee7d78
esi 0x31392774
ebp 0x19f448
esp 0x19f3f0
eip 0x7677ddc2
eflags 0x216
cs 0x23
fs 0x53
gs 0x2b
I believe that problem might lie in the way I pass these strings to procedure, but I can't see what my code does different than that C# application.
Library have a few other procedures, I can call DLL_Version with no problems like so:
lib := syscall.NewLazyDLL("Library.dll")
verProc := lib.NewProc("DLL_Version")
var version float64
verProc.Call(uintptr(unsafe.Pointer(&version)))
log.Printf("DLL version: %f
", version)
Outputs:
2018/09/10 09:13:11 DLL version: 1.250000
EDIT: I believe that I found out what causes the exception. It seems that when called from my code, 2nd and 3rd parameters for this procedure, which should be pointers to string buffers, are instead pointers to pointers on these buffers, if I break on the beginning of procedure and patch this manually, code runs and terminates correctly. I still did not found a reason why this happens, and how to fix it though.
EDIT2: Apparently my previous assessment of this case was invalid. I was able to stop program from throwing exception, but I analyzed assembly and it turned out it was only due to program exiting before this exception was thrown, and instead of exception I got normal error code about invalid string.
While I'm not really good at understanding disassembled code, it seems that problem might indeed be caused by calling convention mismatch. At the beginning of procedure code, when called from working program EAX, EBX, ECX and EDX registers are empty, meanwhile when called from my code, only EAX and ECX are empty, EDX holds something but EBX points to Calc procedure pointer in my executable. Later in the DLL there is a part which checks if EBX is empty and throws exception if not.
EDIT 3: Well, that seems to also be unrelated, I'm aware that there is too little information for anyone to be able to make any guess as to what is going on. So I'll try to track where this exception comes from exactly and come back to this question.
