How to determine Windows process bitness in Java with JNA?

Question

I'm writing a Java method to determine the bitness of a specified Windows process identified by PID. The code calls Win32 API functions through JNA. My attempt is below, but it always returns 32 even when given the PID of a 64 bit process. The code path is always the same (see the comments in the code snippet).

I'm not sure if the approach is conceptually flawed or if there is a bug in the implementation.

The code is running on 64-bit Windows 7 with a 32-bit JRE. What am I doing wrong?

import com.sun.jna.platform.win32.Kernel32;
import com.sun.jna.platform.win32.WinBase.SYSTEM_INFO;
import com.sun.jna.platform.win32.WinNT;
import com.sun.jna.ptr.IntByReference;

public class Test
{

  public static void main(String[] args)
  {
    int pid;

    pid = 10340;
    System.out.println(pid + " bitness = " + getProcessBitness(pid));
    pid = 15116;
    System.out.println(pid + " bitness = " + getProcessBitness(pid));
  }

  /**
   * Given a process ID, determine the bitness of the process.
   * 
   * @param pid
   * @return 32 or 64
   */
  public static int getProcessBitness(int pid)
  {
    Kernel32 kernel32 = Kernel32.INSTANCE;
    IntByReference ref = new IntByReference();

    WinNT.HANDLE hProcess = kernel32.OpenProcess(WinNT.PROCESS_TERMINATE, false, pid);

    // See https://docs.microsoft.com/en-us/windows/desktop/api/wow64apiset/nf-wow64apiset-iswow64process
    kernel32.IsWow64Process(hProcess, ref);
    boolean isWow64 = (ref.getValue() == 1);

    if (isWow64)
      // WOW64 is the x86 emulator that allows 32-bit Windows-based applications to run seamlessly on 64-bit Windows
      return 32;  // This never happens
    else
    {
      // The process bitness matches the OS bitness
      int osBitness;

      // See https://docs.microsoft.com/en-us/windows/desktop/api/sysinfoapi/nf-sysinfoapi-getnativesysteminfo
      SYSTEM_INFO systemInfo = new SYSTEM_INFO();
      kernel32.GetNativeSystemInfo(systemInfo);
      if (systemInfo.processorArchitecture.pi.wProcessorArchitecture.intValue() == 0)
        osBitness = 32;  // This code path is always taken for both 32 and 64 bit processes
      else
        osBitness = 64;  // This never happens
      return osBitness;
    }
  }

}

Answer 1

Thanks to Remy Lebeau, this is the corrected code:

  /**
   * Given a process ID, determine the bitness of the process.
   * 
   * @param pid
   * @return 32 or 64
   */
  public static int getProcessBitness(int pid)
  {
    Kernel32 kernel32 = Kernel32.INSTANCE;
    IntByReference ref = new IntByReference();

    WinNT.HANDLE hProcess = kernel32.OpenProcess(WinNT.PROCESS_QUERY_LIMITED_INFORMATION, false, pid);

    // See https://docs.microsoft.com/en-us/windows/desktop/api/wow64apiset/nf-wow64apiset-iswow64process
    kernel32.IsWow64Process(hProcess, ref);
    boolean isWow64 = (ref.getValue() == 1);

    if (isWow64)
      // WOW64 is the x86 emulator that allows 32-bit Windows-based applications to run seamlessly on 64-bit Windows
      return 32;
    else
    {
      // The process bitness matches the OS bitness
      int osBitness;

      // See https://docs.microsoft.com/en-us/windows/desktop/api/sysinfoapi/nf-sysinfoapi-getnativesysteminfo
      SYSTEM_INFO systemInfo = new SYSTEM_INFO();
      kernel32.GetNativeSystemInfo(systemInfo);

      int processorArchitecture = systemInfo.processorArchitecture.dwOemID.intValue() & 0xFFFF;
      if (processorArchitecture == 0) // PROCESSOR_ARCHITECTURE_INTEL = x86
        osBitness = 32;
      else
        osBitness = 64;
      return osBitness;
    }
  }