getprocessid.c

static DWORD GetProcessId(HANDLE hProcess)
{
	typedef DWORD (WINAPI *pfnGPI)(HANDLE);
	typedef ULONG (WINAPI *pfnNTQIP)(HANDLE, ULONG, PVOID, ULONG, PULONG);

	static int first = 1;
	static pfnGPI GetProcessId;
	static pfnNTQIP ZwQueryInformationProcess;

	if (first) {
		first = 0;

		GetProcessId = (pfnGPI)GetProcAddress(
		    GetModuleHandle("KERNEL32.DLL"), "GetProcessId");
		if (!GetProcessId)
			ZwQueryInformationProcess = (pfnNTQIP)GetProcAddress(
			    GetModuleHandle("NTDLL.DLL"),
			    "ZwQueryInformationProcess");
	}

	if (GetProcessId)
		return GetProcessId(hProcess);

	if (ZwQueryInformationProcess) {
		struct {
			PVOID Reserved1;
			PVOID PebBaseAddress;
			PVOID Reserved2[2];
			ULONG_PTR UniqueProcessId;
			PVOID Reserved3;
		} pbi;
		ZwQueryInformationProcess(hProcess, 0, &pbi, sizeof(pbi), 0);
		return pbi.UniqueProcessId;
	}

	return 0;
}