DactJump/main.c

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

typedef BOOL (WINAPI *GETVERSIONEXA)(LPOSVERSIONINFOA);

BOOL WINAPI FakeGetVersionExA(LPOSVERSIONINFOA lpVersionInformation)
{
    if (!lpVersionInformation) return FALSE;

    lpVersionInformation->dwMajorVersion = 5;
    lpVersionInformation->dwMinorVersion = 1;
    lpVersionInformation->dwBuildNumber  = 2600;
    lpVersionInformation->dwPlatformId   = VER_PLATFORM_WIN32_NT;

    if (lpVersionInformation->dwOSVersionInfoSize == sizeof(OSVERSIONINFOA))
        lstrcpyA(lpVersionInformation->szCSDVersion, "Service Pack 3");

    return TRUE;
}

void PatchGetVersionEx()
{
    HMODULE hKernel;
    FARPROC real;
    DWORD oldProtect;
    BYTE *p;
    DWORD rel;

    hKernel = GetModuleHandleA("kernel32.dll");
    if (!hKernel)
        return;

    real = GetProcAddress(hKernel, "GetVersionExA");
    if (!real)
        return;

    // Allow writing to the first 5 bytes
    if (!VirtualProtect((LPVOID)real, 5, PAGE_EXECUTE_READWRITE, &oldProtect))
        return;

    p = (BYTE*)real;
    rel = (DWORD)FakeGetVersionExA - ((DWORD)real + 5);

    p[0] = 0xE9;               // JMP rel32
    *(DWORD*)(p + 1) = rel;    // Write relative offset

    // Restore protection
    VirtualProtect((LPVOID)real, 5, oldProtect, &oldProtect);
}

int WINAPI WinMain(HINSTANCE hInst, HINSTANCE hPrev, LPSTR lpCmd, int nShow)
{
    const char targetExe[] = "dactyloidae.exe";
    char exePath[MAX_PATH];
    char *p;
    STARTUPINFOA si;
    PROCESS_INFORMATION pi;

    PatchGetVersionEx();

    GetModuleFileNameA(NULL, exePath, MAX_PATH);

    p = strrchr(exePath, '\\');
    if (!p)
        return 0;

    lstrcpyA(p + 1, targetExe);

    ZeroMemory(&si, sizeof(si));
    ZeroMemory(&pi, sizeof(pi));
    si.cb = sizeof(si);

    if (!CreateProcessA(exePath, NULL, NULL, NULL, FALSE, 0, NULL, NULL, &si, &pi))
    {
        MessageBoxA(NULL, "Failed to launch Dactyloidae.", "Error", MB_ICONERROR);
        return 0;
    }

    CloseHandle(pi.hThread);
    CloseHandle(pi.hProcess);

    return 0;
}