Creating DLL's

Introduction

I greatly prefer a UNIX development environment, but sometimes It seems I'm almost forced to develop in Visual Studio (I.E building reflective DLLs). Here are some notes on building DLL's with Visual Studio.

Creating a DLL

To create a DLL in Visual Studio click: Create a Project, set the programming language to C++, and select Dynamic Link Library (DLL).

Adding external functions.

To add an external function use the extern keyword

extern __declspec(dllexport) BOOL ReflectiveFunction() {
}

Template

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

VOID PayloadFunction() {

    MessageBoxA(NULL, "Foo", "Bar", MB_OK | MB_ICONINFORMATION);
}

BOOL APIENTRY DllMain(HMODULE hModule, DWORD dwReason, LPVOID lpReserved) {

    switch (dwReason)
    {
        case DLL_PROCESS_ATTACH:
            PayloadFunction();
            break;
        case DLL_THREAD_ATTACH:
        case DLL_THREAD_DETACH:
        case DLL_PROCESS_DETACH:
            break;
    }
    return TRUE;
}


extern __declspec(dllexport) BOOL ReflectiveFunction() {
}

Extra

Best Practices

Dynamic-Link Library Best Practices - Win32 appsMicrosoftLearn

Makefile

I know I'll be looking for this somewhere so here's the Makefile. If developing on linux, it's crucial we compile the DLL correctly.

x86_64-w64-mingw32-gcc LdrDll.c -s -w -Wall -Wextra -masm=intel -shared -fPIC -e DllMain -Os -fno-asynchronous-unwind-tables Source/* -I Include -o Reflective.dll -lntdll -luser32 -DWIN_X64