About a year ago, I was reading the Windows Internals when I came in the chapter about Wow64, so I thought to myself: “Oh my… That’s a sort of thing that will bring us some issues.”
This week I’ve installed a Vista x64 copy on my computer to do some tests and I attempted to anticipate the problems I would have when it would be released. I almost had no problems. Actually, I had to configure some shortcuts to certain programs with compatibility mode set to Windows XP SP2. This is because these programs showed the message: “This program is not compatible with Windows 6.0”
After installing the Visual Studio 2005, DDK do Windows 2003 Server and DDKBuild, everything was working fine. A project was created, compiled and debugged in Visual Studio without problems. I also compiled a DDK example from the command line and also everything was OK. But at the time I was compiling one of the examples that I’ve already made available at the site using DDKBuild, I got the following error message:
'ddkbuild' is not recognized as an internal or external command
Executing the DDKBuild in a command prompt, it worked fine, but same error was always showing at the Visual Studio. After pooling out some hair, I tried to open the file DDKBuild.cmd from Visual Studio, that is, by selecting Open… from File menu and so on. When I got into the System32 directory, I saw that the file I was looking for was not there as it should be, at least, not for Visual Studio.
It took some time, but the penny dropped. Visual Studio is a 32 bit process and fell in the Wow64 (Windows-on-Windows 64) rules for File System redirection. For those who do not know, to maintain compatibility with the past, 64-bit platforms still use the directory C: \Windows\System32 folder to put the system DLLs, even though they were 64-bits.
But what happens with 32-bit system DLLs? Thirty-two bit processes still need to load these DLLs. When a 32-bit process tries to access the C:\Windows\System32 directory, the access is redirected by Wow64 to C:\Windows\SysWow64 (C:\Windows\System32\SysWow64 For Windows XP x64). Accesses to the registry are also reflected from 32 bits to 64 bits and vice versa. Please, refer to the MSDN site for Wow64 details.
Once the penny has dropped, it is ridiculous to solve the problem. Simply put a copy of DDKBuild.cmd in the C:\Windows\SysWow64 and everyone will live happily ever after.
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