When using fast forwarding, createThreads() is not called upon FutureCPUs. This causes segment fault as the decoder is initialized in createThreads() and needed when instantiating CPUs. This commit basically fixes this by invoking createThreads() on FutureCPUs after they are created. Change-Id: I812d18f06878f9fc3fa2183a2c8a64d316413398 Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/56812 Reviewed-by: Jason Lowe-Power <power.jg@gmail.com> Maintainer: Jason Lowe-Power <power.jg@gmail.com> Reviewed-by: Luming Wang <wlm199558@126.com> Tested-by: kokoro <noreply+kokoro@google.com>