When I'm trying to attach to the simple binary with DTrace command (sudo dtrace -n 'pid$1:::' ps aux | grep FibbSlow | grep -v grep | awk '{print $2}' ) it crashes with various outcomes. This happens on both GHC 8.4.3 from stack and manually built ghc from the master branch.

Crashes:

lastg-mbp:t lastg$ ./FibbSlow.master 55
FibbSlow.master: internal error: scavenge: unimplemented/strange closure type 13369548 @ 0x420021abb0^[[B
    (GHC version 8.7.20180817 for x86_64_apple_darwin)
    Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug

lastg-mbp:t lastg$ ./FibbSlow.stack.8.4 55
FibbSlow.stack.8.4: internal error: scavenge_one: strange object 13369548
    (GHC version 8.4.3 for x86_64_apple_darwin)
    Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug
Abort trap: 6

lastg-mbp:t lastg$ ./FibbSlow.stack.8.4 55
FibbSlow.stack.8.4: internal error: scavenge_one: strange object 13369548
    (GHC version 8.4.3 for x86_64_apple_darwin)
    Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug
Abort trap: 6

lastg-mbp:t lastg$ ./FibbSlow.stack.8.4 55
Segmentation fault: 11

Source code for the binary: https://gist.github.com/last-g/cfddab60a8520eb51214ef2a7bc48ec2