Missing PROGRAMDATA Environment Variable when Chrome invokes a 64 bit binary that is wrongly packaged with Platform = x86 in the wix file

kanish garg 0

Hi everyone!

I have a query around the expansion of the %PROGRAMDATA% environment variable in a 64 bit binary mistakenly packaged with Platform = x86 in the wix file.

Context: Recently, when we released the binary to our customers via Omaha, because of some reason (unknown to us as of now), ExpandEnvironmentStringsA (windows api in our binary) wasn't able to expand the path containing the %PROGRAMDATA% environment variable, which caused multiple issues.

As per my understanding if a process A starts a child process B, environment variables for process A gets passed to process B. In our case, since binary is invoked only via Chrome Native Messaging, Chrome should had passed the %PROGRAMDATA% environment variable to the binary.

Please note that, we identified a issue with the binary that we released. It was a 64 bit binary however the value of platform in the Wix file was set to x86. Afaik, PLATFORM field in the wix file (while packaging) decides the location of the installation i.e ProgramFiles(x86) or ProgramFiles. Basically it decides whether to use the Wow64 subsystem or not. So in our case, 64 bit binary was using windows Wow64 Subsystem, which indeed was not right, however want to understand how it could impact the value of %PROGRAMDATA% environment variable?

Thanks!

RLWA32 43,306 Reputation points

2023-04-26T15:13:22.31+00:00

The file system location (i.e., ProgramFiles (x86) or ProgramFiles) does not determine the bitness of a process. That is determined by the executable file. So a 64-bit executable started from a folder under ProgramFiles (x86) will run as a 64-bit process, not a WOW64 process. A parent process determines the environment that a child process will receive. If you look at the documentation of the CreateProcessW function for the lpEnvironment parameter it says "A pointer to the environment block for the new process. If this parameter is NULL, the new process uses the environment of the calling process." So inheritance of the parent process environment is not automatic. A parent process could create and pass a customized environment block to a child process.
RLWA32 43,306 Reputation points

2023-04-27T12:35:05.45+00:00

You can use Microsoft's Process Explorer to view the environment variables of a running process.
kanish garg 0 Reputation points

2023-07-04T17:46:46.0833333+00:00

Thanks RLWA32! Indeed the file system location does not determine whether the process will use WOW64 subsystem or not.

What issues can happen when a 64 bit binary is packaged as 32 bit with Wix (i.e PLATFORM = x86)? Does Wow64 subsystem be used in this case?
RLWA32 43,306 Reputation points

2023-07-05T09:16:45.07+00:00

The bitness of the installed executable is the determining factor. A 64-bit executable runs as a 64-bit process and a 32-bit executable runs as a 32-bit process under WOW64.

The value of the %PROGRAMDATA% environment variable is the same for 64-bit and 32-bit processes.

Share via

Missing PROGRAMDATA Environment Variable when Chrome invokes a 64 bit binary that is wrongly packaged with Platform = x86 in the wix file