How to launch a Windows process as 64-bit from 32-bit code?

Question

To pop up the UAC dialog in Vista when writing to the HKLM registry hive, we opt to not use the Win32 Registry API, as when Vista permissions are lacking, we'd need to relaunch our entire application with administrator rights. Instead, we do this trick:

ShellExecute(hWnd, "runas" /* display UAC prompt on Vista */, windir + "\\Reg", "add HKLM\\Software\\Company\\KeyName /v valueName /t REG_MULTI_TZ /d ValueData", NULL, SW_HIDE);

This solution works fine, besides that our application is a 32-bit one, and it runs the REG.EXE command as it would be a 32-bit app using the WOW compatibility layer! :( If REG.EXE is ran from the command line, it's properly ran in 64-bit mode. This matters, because if it's ran as a 32-bit app, the registry keys will end up in the wrong place due to registry reflection.

So is there any way to launch a 64-bit app programmatically from a 32-bit app and not have it run using the WOW64 subsystem like its parent 32-bit process (i.e. a "*" suffix in the Task Manager)?

Answer 1

Whether a 32-bit or 64-bit native (unmanaged) program is run depends solely on the executable. There are two copies of reg.exe, in C:\Windows\System32 (64-bit) and C:\Windows\SysWOW64 (32-bit). Because you don't specify a path, you're getting whatever appears first in the PATH environment variable, which is the 32-bit version for a 32-bit process.

You should really factor this function out into a separate program or COM object, and mark the program with a manifest, or launch the COM object using the COM elevation moniker.