Now I think that it is closer to what I need for golang runtime, at least it works here.
Could you take a look?

please bear with me. I'm currently busy with the upcoming Genode
release. I'll be happy to give you feedback by mid of next week.

I just ported current set of patches to 20.11.
please, take a look at https://github.com/tor-m6/genode.git branch 20.11
main implementation of mmap part temporary in 1 file and 1 patch
anon_mmap.cc from
https://github.com/tor-m6/genode/commit/cf79a564e1b004fef5660e84d01d6c2906742d3f
and genode files minor modifications
https://github.com/tor-m6/genode/commit/41b57fd06516c9b33b4b06e1f91cb134a3da8ce9