GHC provides built in profiling support that can export a JSON file. In order to do this you need to compile your executable with profiling support and then pass the -pj RTS flag to the executable.

This will produce a my-binary.prof file in the current directory which you can import into speedscope.

See the GHC manual page on profiling for more extensive information on the command line flags available.

$ ghc -prof -fprof-auto -rtsopts Main.hs
$ ./Main  RTS -pj -RTS

$ stack build --profile
$ stack exec -- my-executable  RTS -pj -RTS

stack test --profile --test-arguments " RTS -pj -RTS"