如何在Windows 7 X64 SP1 (X64模式)下直接执行syscall ?

I tried to simulate how the syscall instruction working on Windows 7 X64 (SP1), so I program a 64bit GCC example with MinGW64. As I know, for Windows, all syscall entry point is within ntdll.dll or ntdll32.dll (in this case, we just care for ntdll.dll).I tried to simulate how the syscall instruction