Hi all, I thought for a long while that if you wanted to profile GHC itself then you had to build a profiled version of HEAD. However, this isn't true. The easiest way to profile GHC itself is to write a simple GHC API application and compile that with profiling. Normal GHC distributions come with profiling versions of the ghc library so you can use this to profile released versions of the compiler. For example, here is a simple program that Andreas created when I suggested he did this. https://gist.github.com/mpickering/e13f343f2b35b51693d15582180b1c02 You can specify whatever options you want to start the session, you might imagine compiling a package with cabal and copying the command line flags from there in order to set up a session correctly. Cheers, Matt