#include <stdio.h>
#include <errno.h>

#if defined(__linux__)

#include <unistd.h>
#define GETPID 39

pid_t
getpid_syscall (void)
{
  pid_t pid = syscall(GETPID);
  return pid;
}

#elif defined(_WIN32)

#include <windows.h>
#include <winternl.h>
#include <conio.h>

/* we define a pid integer to be of DWORD size */
typedef DWORD pid_t;

__declspec(noinline)
__declspec(naked)
NTSTATUS
CallNtQueryInformationProcess(HANDLE ProcessHandle, PROCESSINFOCLASS ProcessInformationClass, PVOID ProcessInformation, ULONG ProcessInformationLength, PULONG ReturnLength)
{
  __asm {
    mov eax, 0x00a1      /* TODO: syscall nummer hier */
    mov edx, 0x7FFE0300  /* KUSER_SHARED_DATA syscall stub */
    call dword ptr [edx] /* call the stub code */

    ret
  }
}

pid_t
getpid_syscall (void)
{
  /* TODO: call CallNtQueryInformationProcess with the right parameters and
   *       extract and return the process id
   *
   * see: https://msdn.microsoft.com/en-us/library/windows/desktop/ms684280(v=vs.85).aspx
   */
  return CallNtQueryInformationProcess();
}

#else
/* if neither linux, nor windows, we can't proceed. */
#error neither windows nor linux?
#endif

int
main (void)
{
  /* produce user mode API pid */
  pid_t pid_getpid  = getpid();
  /* produce syscall API pid */
  pid_t pid_syscall = getpid_syscall();

  /* error handling is always useful */
  if (pid_syscall <= 0)
    {
      perror("getpid_syscall");
      return 1;
    }

  /* print both and exit */
  printf("%d\n%d\n", pid_getpid, pid_syscall);
  return 0;
}