Compile DLL with a static library using gcc (mingw32)

Question

I've a static library let's call it libsecondary.a generated by a external tool, i.e CGO. I want to generate a dynamic library while including "libsecondary.a" as a dependency, I export a function called OnProcessInit() inside libsecondary.h and call it on the DLL_PROCESS_ATTACH event.

I tried to generate the shared library but seems to fail using x86_64-w64-mingw32 -shared -L. -lsecondary -static-libgcc -static-libstdc++ -static .\dllmain.c

The error output is dllmain.c:(.text+0x9b): undefined reference to `OnProcessInit', what's going on?

This is the header file libsecondary.h

/* Code generated by cmd/cgo; DO NOT EDIT. */

/* package command-line-arguments */


#line 1 "cgo-builtin-export-prolog"

#include <stddef.h>

#ifndef GO_CGO_EXPORT_PROLOGUE_H
#define GO_CGO_EXPORT_PROLOGUE_H

#ifndef GO_CGO_GOSTRING_TYPEDEF
typedef struct { const char *p; ptrdiff_t n; } _GoString_;
#endif

#endif

/* Start of preamble from import "C" comments.  */




/* End of preamble from import "C" comments.  */


/* Start of boilerplate cgo prologue.  */
#line 1 "cgo-gcc-export-header-prolog"

#ifndef GO_CGO_PROLOGUE_H
#define GO_CGO_PROLOGUE_H

typedef signed char GoInt8;
typedef unsigned char GoUint8;
typedef short GoInt16;
typedef unsigned short GoUint16;
typedef int GoInt32;
typedef unsigned int GoUint32;
typedef long long GoInt64;
typedef unsigned long long GoUint64;
typedef GoInt64 GoInt;
typedef GoUint64 GoUint;
typedef size_t GoUintptr;
typedef float GoFloat32;
typedef double GoFloat64;
#ifdef _MSC_VER
#include <complex.h>
typedef _Fcomplex GoComplex64;
typedef _Dcomplex GoComplex128;
#else
typedef float _Complex GoComplex64;
typedef double _Complex GoComplex128;
#endif

/*
  static assertion to make sure the file is being used on architecture
  at least with matching size of GoInt.
*/
typedef char _check_for_64_bit_pointer_matching_GoInt[sizeof(void*)==64/8 ? 1:-1];

#ifndef GO_CGO_GOSTRING_TYPEDEF
typedef _GoString_ GoString;
#endif
typedef void *GoMap;
typedef void *GoChan;
typedef struct { void *t; void *v; } GoInterface;
typedef struct { void *data; GoInt len; GoInt cap; } GoSlice;

#endif

/* End of boilerplate cgo prologue.  */

#ifdef __cplusplus
extern "C" {
#endif

extern __declspec(dllexport) void OnProcessInit();

#ifdef __cplusplus
}
#endif

And this is dllmain.c

#include <windows.h>
#include <stdio.h>
#include "libsecondary.h"

BOOL WINAPI DllMain(HINSTANCE hinstDLL, DWORD fdwReason, LPVOID lpReserved)
{
    switch (fdwReason)
    {
    case DLL_PROCESS_ATTACH:
        printf("It works i guess");
        OnProcessInit();
        break;

    case DLL_THREAD_ATTACH:
        break;

    case DLL_THREAD_DETACH:
        break;

    case DLL_PROCESS_DETACH:
        break;
    }

    return TRUE;
}

This is the exported golang function (the one that I compile using go build -buildmode=c-archive)

package main
import "C"
import (
    "unsafe"
    "syscall"
)

//export OnProcessInit
func OnProcessInit() {
    const (
        NULL  = 0
        MB_OK = 0
    )
    caption := "Hola"
    title := "desdegoo"
    ret, _, _ := syscall.NewLazyDLL("user32.dll").NewProc("MessageBoxW").Call(
        uintptr(NULL),
        uintptr(unsafe.Pointer(syscall.StringToUTF16Ptr(caption))),
        uintptr(unsafe.Pointer(syscall.StringToUTF16Ptr(title))),
        uintptr(MB_OK))

    if ret != 1 {
        return
    }
    return 
}

func main() {}

Answer 1

Wow, the answer was the argument position,

x86_64-w64-mingw32 -shared -static-libgcc -static-libstdc++ -static .\dllmain.c .\libsecondary.a

If you type it backwards it won't find references from libsecondary.a, jeez...

Also the above code runs into a deadlock upon getting loaded, because syscall.NewLazyDLL calls LoadLibraryA, and it's locked inside DLL_PROCESS_ATTACH, so the way to go is to CreateThread and run the golang exported function inside the thread :)