Cross compiling golang with cgo for Windows target on macOS host

Question

I am on macOS and trying to cross compile golang (CGO 1.10) executable for Windows using mingw-w64 installed from homebrew.

I have golang package with only one function (SimpleQRDecode) that calls other function from my c++ source (FindAndDecodeQR, uses zxing c++ port).

Compiling ZXing sources is fine (x86_64-w64-mingw32-g++)
Compiling qrcode.cpp is fine (x86_64-w64-mingw32-g++)
Successfully merged all objects (zxing + my) into static library (x86_64-w64-mingw32-ar)
Successfully called ranlib on static library (x86_64-w64-mingw32-ranlib)
FAILED to call CGO_ENABLED=1 CXX="x86_64-w64-mingw32-g++" CXX_FOR_TARGET="x86_64-w64-mingw32-g++" CC="x86_64-w64-mingw32-gcc" CC_FOR_TARGET="x86_64-w64-mingw32-gcc" GOOS=windows GOARCH=amd64 go build -x

go build output consists of tons of unresolved symbol messages like

libmyqr.a(qrcode.o):qrcode.cpp:(.text+0x79): undefined reference to `operator new(unsigned long long)'
libmyqr.a(qrcode.o):qrcode.cpp:(.text+0x2cb): undefined reference to `std::string::length() const'
libmyqr.a(qrcode.o):qrcode.cpp:(.text+0x4a7): undefined reference to `__cxa_begin_catch'
libmyqr.a(BinaryBitmap.cpp.obj):BinaryBitmap.cpp:(.text+0x5c2): undefined reference to `std::ios_base::Init::~Init()'
libmyqr.a(BinaryBitmap.cpp.obj):BinaryBitmap.cpp:(.xdata+0xc): undefined reference to `__gxx_personality_seh0'

qrcode.go:

package qrcode

/*
#cgo CFLAGS: -I../../native/prefix/include -I../../libmyqr -fPIC
#cgo CXXFLAGS: -I../../native/prefix/include -I../../libmyqr -fPIC
#cgo LDFLAGS: -L../../libmyqr -lmyqr -lstdc++
#include <stdlib.h>
#include <qrcode.h>
*/
import "C"

import (
    "errors"
    "fmt"
    "unsafe"
)

func SimpleQRDecode(rasterData []byte, width, height int) (string, bool, error) {
    res := C.FindAndDecodeQR((*C.char)(unsafe.Pointer(&data[0])), C.int(len(data)), C.int(width), C.int(height))

qrcode.h:

#ifdef __cplusplus
extern "C" {
#endif

const char* FindAndDecodeQR(char *raster, int size, int width, int height);


#ifdef __cplusplus
}
#endif

qrcode.cpp:

#include "qrcode.h"

#include <sstream>

#include <zxing/ZXing.h>
#include <zxing/Binarizer.h>
#include <zxing/BinaryBitmap.h>
#include <zxing/Result.h>
#include <zxing/qrcode/QRCodeReader.h>
#include <zxing/common/GreyscaleRotatedLuminanceSource.h>
#include <zxing/common/GlobalHistogramBinarizer.h>

const char* FindAndDecodeQR(char *raster, int size, int width, int height) {
    // GreyscaleLuminanceSource

    std::ostringstream resStream;

    try {
        zxing::ArrayRef<char> image(raster, size);
        zxing::Ref<zxing::GreyscaleRotatedLuminanceSource> source(new zxing::GreyscaleRotatedLuminanceSource(image, width, height, 0, 0, width, height));

libmyqr.a - static library made of all zxing compiled objects + qrcode.cpp.o

ivoszz ivoszz · Accepted Answer · 2018-03-27T16:14:38

It is probably not what you want to hear but the easiest way to cross compile to windows on Mac is to build a DLL library from your c/c++ code and handle this DLL library from your go code. In this situation you even don't need CGO_ENABLED=1.

The go code can look like this (not tested):

// +build windows

package qrcode

import (
    "errors"
    "fmt"
    "syscalls"
    "unsafe"
)

var modYourPkg = syscall.NewLazyDLL("yourpkg.dll")

var procFindAndDecodeQR = modYourPkg.NewProc("FindAndDecodeQR")

func SimpleQRDecode(rasterData []byte, width, height int) (string, bool, error) {
    res, _, _ := procFindAndDecodeQR.Call(
        uintptr(unsafe.Pointer(&rasterData[0])),
        uintptr(len(data)),
        uintptr(width),
        uintptr(height),
    )
    ...
}

See more in documentation to the syscall package.

Cross compiling golang with cgo for Windows target on macOS host

1 Answers