Delphi - Wow64EnableWow64FsRedirection Error 32-bit OS

Question

I have a code exmple.

unit Unit1;

interface

uses
...

type
...

function Wow64EnableWow64FsRedirection(Wow64FsEnableRedirection: BOOL): BOOL; stdcall;

var
...

implementation

{$R *.dfm}

uses
...

function Wow64EnableWow64FsRedirection; external kernel32 name 'Wow64EnableWow64FsRedirection';

procedure LaunchOSK;
begin
  Wow64EnableWow64FsRedirection(False);
  try
    ShellExecute(0, 'OPEN', PChar('osk.exe'), nil, nil, SW_SHOWNORMAL);
  finally
    Wow64EnableWow64FsRedirection(True);
  end;
end;

end.

This code works fine in 64-bit OS. However, naturally when you try to use this in a 32-bit OS (XP) you get an error message (The procedure entry point Wow64Enable64FsRedirection could not be located in the dynamic link library kernel32.dll.). If you isolate Wow64EnableWow64FsRedirection and just run ShellExecute it launches fine.

I have beaten my head the past 2 days trying different things I have Googled and not one them of works as far as safely starting OSK in both 32 and 64 bit. Even a well known Delphi guru's suggestion does not work.

I do not need a lecture about disabling Wow64EnableWow64FsRedirection. Since it is temporary no harm no foul.

What I need is understanding how I can take this code and isolate the Wow64Enable64FsRedirection interface procedure and its accompanying implementation part and the necessary parts of the LaunchOSK procedure when the application is running on XP for example. Is this possible??? Compiler statements are useless, right?

If this is not possible then I will have to resort in producing 2 apps (one for XP and the other for 64 bit) which is a last resort.

Thanks in advance.

Answer 1

You can use dynamic loading and simply check whether the GetProcAddress function returns a valid function address.

Or you can use delayed loading and call the imported function only if the OS version and bitness matches necessary requirements.

Answer 2

Your code uses load time linking. The imported function must be present in the system or your executable will not start.

Instead you need to use run time linking. Use LoadLibrary and GetProcAddress to link to the function. If GetProcAddress fails to find the function then it isn't available and of course you don't need to call it because you are on a 32 bit OS.

The right way to do this though is to spawn a 64 bit process which can then launch the OSK process. And if ever you really do need to disable redirection do heed the documentation which tells you to use Wow64DisableWow64FsRedirection.

Finally it's always best to use CreateProcess to launch a process. There's nothing to be gained from involving the shell and file associations. Why ask the shell to call CreateProcess when you can do so directly?

OK, that's normally good advice, but once again, OSK is special. See Delphi - On Screen Keyboard (osk.exe) works on Win32 but fails on Win64.