For COM server and registry key redirection, does it need to do file path redirection translation?

Question

Forgive me if the title is not so accurate.

I have met some problem when I am doing something related to COM server and registry redirection and not quite sure is my understanding is correct or not. Hoping anyone could share some light on it. Thanks in advance.

Basically a COM server has been registered in the registry before anyone can use its service. On a 64bit Windows OS, there could be 2 possible views in the registry table, one is for default and the other for the WOW64 view. For example, first registry key is: COMPUTER\HKEY_LOCAL_MACHINE\SOFTWARE\Classes\CLSID{GUID}\LocalServer32 and the other is: COMPUTER\HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Classes\CLSID{GUID}\LocalServer32. And depends on the process bitness (64bit vs. 32bit) that either one can be read by default, and also we can use KEY_WOW64_64KEY or KEY_WOW64_32KEY (as: http://msdn.microsoft.com/en-us/library/windows/desktop/aa384129(v=vs.85).aspx) to access the other alternative registry key.

What I need is that, I want to get the LocalServer32 executable file by reading the registry key and this can work. The problem is that, for the executable file path I read back, do I need to do the file path translation (in order to get the correct value) depending on which view I get the value from? For example, if the file path is got from COMPUTER\HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Classes\CLSID{GUID}\LocalServer32 and the file path is: C:\Windows\System32\abc.exe, do I need to translate the path to: C:\Windows\SysWow64\abc.exe? Or do I need to translate C:\Program Files\abc.exe to C:\Program Files(x86).exe?

Another question is that, if, for some registry key for COM, the values set in the two Views are different (for example, one has C:\Program Files\abc.exe and the other has C:\Program Files(x86)\abc.exe), then when the COM server is started, how could svchost.exe know which one to start, C:\Program Files\abc.exe or C:\Program Files(x86)\abc.exe? Does anyone know the logic for svchost.exe to determine this? Use the first one if it exists otherwise use the second one?

Thanks a lot.

Answer 1

A 64-bit version of Windows already has all the features in place to make it unnecessary for you to take care of it yourself. You just need to keep the rules in mind when you troubleshoot problems.

First is the registry redirector, it ensures that a 32-bit client program cannot accidentally read keys that contain configuration information that's only appropriate for 64-bit programs. You already know it, most of the HKLM\Software registry accesses are redirected to HKLM\Software\Wow6432Node. This redirection is already in place when the COM server is registered, a 32-bit installer is automatically redirected to write the keys to Wow6432Node instead. The installer is completely unaware that Wow6432Node even exists. Everything falls together automatically, the installer is redirected and the COM server client is redirected as well. All that you care about is knowing where to look to verify that the install was done properly, you do have to look at HKLM\Software\Wow6432Node\Classes\CLSID with Regedit.exe to find the keys back.

File redirection works much the same way, any access to c:\windows\system32 is redirected to c:\windows\syswow64, from c:\program files to c:\program files (x86). And very similarly, a 32-bit installer doesn't have to know beans about this, it can simply use the legacy 32-bit path names. Same for any 32-bit client program, it will be redirected the same way. All that you care about is knowing where to look for a file to verify the installer.

This can only go wrong if bitness is mixed, a 64-bit program reading registry keys or files installed by a 32-bit program. Or the other way around. Like it does with your troubleshooting tools, like Explorer, Regedit and SysInternals' Process Monitor. In general something that should be strongly avoided in COM, most servers are in-process servers and running 32-bit code in a 64-bit process is not possible. The biggest reason that the registry and file redirectors exist in the first place.