Hi all, I wanted to try our codebase with 8.6. I happened to already have 8.6.0.20180714 ready so I started with that. Compilation went well but I got a segfault when running a benchmark we have with profiling on. GDB told me the segfault was in stg_ap_ppppp_info in AutoApply.cmm which as I understand is generated. Strange but OK... I decided to try unprofiled with LLVM to see if some LLVM issue we had with current version (7.10.x) has gone away. Sadly I encountered a segfault during regular compilation (clean build, LLVM 6.0). I had no debugging symbols. Next I decided to try the beta1 version. I copied mk/build.mk.sample into mk/build.mk and added the following: GhcDebugged = YES GhcStage1HcOpts = -DDEBUG GhcStage2HcOpts = -DDEBUG I checked out the 8.6.1-beta1 tag then ran following. fuuzetsu@rubin:~/programming/ghc$ echo $PREFIX /usr/local/ghc/ghc-8.6.1-beta1 fuuzetsu@rubin:~/programming/ghc$ ./configure --prefix=$PREFIX && make -j4 && make install After some time I was met with: /usr/bin/ld.gold: error: cannot find -lHSrts_thr_debug_p Also a long chain of messages about undefined refs you can find at [1]. Considering I haven't touched any settings beyond adding debug flags, it surprised me a little that I can't build successfully. Please advise and feel free to ask for any specs. uname -a: Linux rubin.tsuru.it 4.15.0-30-generic #32~16.04.1-Ubuntu SMP Thu Jul 26 20:25:39 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux [1]: https://gist.github.com/Fuuzetsu/7a65a963dd625386d13938ba1e22af5c -- Mateusz K.