Alexey Solofnenko blog

Ever wondered if your policy assemblies work?

.Net assemblies remember what versions of referenced assemblies they were built with. In general it is a good thing, but it creates its own problems when building a product that consists of many separate parts. In the interest of QA we often build mismatched package builds with some of the application products built with earlier versions of core libraries. Fortunately our build scripts (directly from VisualStudio) generate all necessary policy assemblies for previous and the current releases and installer puts them into GAC.

At first there were rumors that one of applications (developed in a different office and built on its own schedule) does not start in mismatched builds. In the beginning the warnings were dismissed because the APIs were not stable, but later it became apparent that something is wrong. And finally the problem came to me...

After enabling assembly loader log, it showed that policy assembly was recognized and the redirect actually happened, but the target assembly was not found even it was right there in the GAC. However there was a message that the platform was locked to the policy assembly platform. This particular assembly had native DLLs attached to it, so its platform was not a generic "MSIL", but "x86" and this is why it could not be found.

To test this idea I regenerated policy file with matching platform, but how to install it into GAC? Removing old policy was not possible - it was locked by installer. Fortunately Cygwin`s Midnight Commander sees real file system and ignores all Microsoft crap and I was able to remove the assembly directly from hard drive and install a new one into GAC. And it helped - the application started and worked without problems.

The policy generation (and some other "black magic" staff, including support for linked resources) is done via an include in our project files and is a part of another utility project. After that project rebuild, our automatic build picked it up and certified all dependent projects to pass unit tests. Now all our policy assembly platform match their assembly's platform and everything quiet in our kingdom.