## Friday, November 02, 2012

### DLL Hell

I recently downloaded GNU Solfege ear training software. On trying to run it I encountered the dreaded message "The procedure entry point deflateSetHeader could not be located in the dynamic link library zlib1.dll."

So Solfege was presumably getting handed an outdated version of the dll to run, instead of the version installed in its bin folder. A typical DLL hell issue.

It's been years since I last recall fighting with DLL hell. So I guess that while .Net doesn't completely solve DLL hell, it has certainly mitigated the problem.

I first tried looking for the dll in c:\windows\system32. But there was no copy of zlib1 there.

I thought that the wrong DLL version might be somewhere on the environment PATH. So I then wrote the following Powershell script to search for the dll:

$paths = ($env:path -split ';' | % { $_ -replace '%SystemRoot%','c:\windows' } ) Get-ChildItem -path$paths -filter 'zlib1.dll'


This script showed that one of the Roxio folders is in the path and contains a zlib1 dll from 2010. So I removed Roxio from the environment path. But still I got that error message.

[If I'd thought to first check what order Windows looks for dll's in, I could have saved myself the trouble. It looks like the PATH variable is the last place searched.]

So where could the culprit be?

I then opened up the Process Explorer utility from the brilliant SysInternals suite. One of my most-used features in Process Explorer is the "Find handle or dll" menu item (CTRL + F). This showed that zlib1.dll was in c:\windows\SysWOW64...

That version of zlib1.dll was ancient - last modified in 2007. So I backed it up and copied a much newer version across.

And now GNU Solfege is working again!